Ticket #49028: wp-db.php

<?php
/**
 * WordPress DB Class
 *
 * Original code from {@link http://php.justinvincent.com Justin Vincent (justin@visunet.ie)}
 *
 * @package WordPress
 * @subpackage Database
 * @since 0.71
 */

/**
 * @since 0.71
 */
define( 'EZSQL_VERSION', 'WP1.25' );

/**
 * @since 0.71
 */
define( 'OBJECT', 'OBJECT' );
// phpcs:ignore Generic.NamingConventions.UpperCaseConstantName.ConstantNotUpperCase
define( 'object', 'OBJECT' ); // Back compat.

/**
 * @since 2.5.0
 */
define( 'OBJECT_K', 'OBJECT_K' );

/**
 * @since 0.71
 */
define( 'ARRAY_A', 'ARRAY_A' );

/**
 * @since 0.71
 */
define( 'ARRAY_N', 'ARRAY_N' );

/**
 * WordPress Database Access Abstraction Object
 *
 * It is possible to replace this class with your own
 * by setting the $wpdb global variable in wp-content/db.php
 * file to your class. The wpdb class will still be included,
 * so you can extend it or simply use your own.
 *
 * @link https://codex.wordpress.org/Function_Reference/wpdb_Class
 *
 * @since 0.71
 */
class wpdb {

        /**
         * Whether to show SQL/DB errors.
         *
         * Default behavior is to show errors if both WP_DEBUG and WP_DEBUG_DISPLAY
         * evaluated to true.
         *
         * @since 0.71
         * @var bool
         */
        var $show_errors = false;

        /**
         * Whether to suppress errors during the DB bootstrapping.
         *
         * @since 2.5.0
         * @var bool
         */
        var $suppress_errors = false;

  /**
         * Whether to suppress filters 'query' filter prior to execution..
         *
         * @since 5.4.0
         * @var bool
         */
        var $suppress_filters = false;

        /**
         * The last error during query.
         *
         * @since 2.5.0
         * @var string
         */
        public $last_error = '';

        /**
         * Amount of queries made
         *
         * @since 1.2.0
         * @var int
         */
        public $num_queries = 0;

        /**
         * Count of rows returned by previous query
         *
         * @since 0.71
         * @var int
         */
        public $num_rows = 0;

        /**
         * Count of affected rows by previous query
         *
         * @since 0.71
         * @var int
         */
        var $rows_affected = 0;

        /**
         * The ID generated for an AUTO_INCREMENT column by the previous query (usually INSERT).
         *
         * @since 0.71
         * @var int
         */
        public $insert_id = 0;

        /**
         * Last query made
         *
         * @since 0.71
         * @var string
         */
        var $last_query;

        /**
         * Results of the last query made
         *
         * @since 0.71
         * @var array|null
         */
        var $last_result;

        /**
         * MySQL result, which is either a resource or boolean.
         *
         * @since 0.71
         * @var mixed
         */
        protected $result;

        /**
         * Cached column info, for sanity checking data before inserting
         *
         * @since 4.2.0
         * @var array
         */
        protected $col_meta = array();

        /**
         * Calculated character sets on tables
         *
         * @since 4.2.0
         * @var array
         */
        protected $table_charset = array();

        /**
         * Whether text fields in the current query need to be sanity checked.
         *
         * @since 4.2.0
         * @var bool
         */
        protected $check_current_query = true;

        /**
         * Flag to ensure we don't run into recursion problems when checking the collation.
         *
         * @since 4.2.0
         * @see wpdb::check_safe_collation()
         * @var bool
         */
        private $checking_collation = false;

        /**
         * Saved info on the table column
         *
         * @since 0.71
         * @var array
         */
        protected $col_info;

        /**
         * Log of queries that were executed, for debugging purposes.
         *
         * @since 1.5.0
         * @since 2.5.0 The third element in each query log was added to record the calling functions.
         * @since 5.1.0 The fourth element in each query log was added to record the start time.
         * @since 5.3.0 The fifth element in each query log was added to record custom data.
         *
         * @var array[] {
         *     Array of queries that were executed.
         *
         *     @type array ...$0 {
         *         Data for each query.
         *
         *         @type string $0 The query's SQL.
         *         @type float  $1 Total time spent on the query, in seconds.
         *         @type string $2 Comma separated list of the calling functions.
         *         @type float  $3 Unix timestamp of the time at the start of the query.
         *         @type array  $4 Custom query data.
         *     }
         * }
         */
        var $queries;

        /**
         * The number of times to retry reconnecting before dying.
         *
         * @since 3.9.0
         * @see wpdb::check_connection()
         * @var int
         */
        protected $reconnect_retries = 5;

        /**
         * WordPress table prefix
         *
         * You can set this to have multiple WordPress installations
         * in a single database. The second reason is for possible
         * security precautions.
         *
         * @since 2.5.0
         * @var string
         */
        public $prefix = '';

        /**
         * WordPress base table prefix.
         *
         * @since 3.0.0
         * @var string
         */
        public $base_prefix;

        /**
         * Whether the database queries are ready to start executing.
         *
         * @since 2.3.2
         * @var bool
         */
        var $ready = false;

        /**
         * Blog ID.
         *
         * @since 3.0.0
         * @var int
         */
        public $blogid = 0;

        /**
         * Site ID.
         *
         * @since 3.0.0
         * @var int
         */
        public $siteid = 0;

        /**
         * List of WordPress per-blog tables
         *
         * @since 2.5.0
         * @see wpdb::tables()
         * @var array
         */
        var $tables = array(
                'posts',
                'comments',
                'links',
                'options',
                'postmeta',
                'terms',
                'term_taxonomy',
                'term_relationships',
                'termmeta',
                'commentmeta',
        );

        /**
         * List of deprecated WordPress tables
         *
         * categories, post2cat, and link2cat were deprecated in 2.3.0, db version 5539
         *
         * @since 2.9.0
         * @see wpdb::tables()
         * @var array
         */
        var $old_tables = array( 'categories', 'post2cat', 'link2cat' );

        /**
         * List of WordPress global tables
         *
         * @since 3.0.0
         * @see wpdb::tables()
         * @var array
         */
        var $global_tables = array( 'users', 'usermeta' );

        /**
         * List of Multisite global tables
         *
         * @since 3.0.0
         * @see wpdb::tables()
         * @var array
         */
        var $ms_global_tables = array(
                'blogs',
                'blogmeta',
                'signups',
                'site',
                'sitemeta',
                'sitecategories',
                'registration_log',
        );

        /**
         * WordPress Comments table
         *
         * @since 1.5.0
         * @var string
         */
        public $comments;

        /**
         * WordPress Comment Metadata table
         *
         * @since 2.9.0
         * @var string
         */
        public $commentmeta;

        /**
         * WordPress Links table
         *
         * @since 1.5.0
         * @var string
         */
        public $links;

        /**
         * WordPress Options table
         *
         * @since 1.5.0
         * @var string
         */
        public $options;

        /**
         * WordPress Post Metadata table
         *
         * @since 1.5.0
         * @var string
         */
        public $postmeta;

        /**
         * WordPress Posts table
         *
         * @since 1.5.0
         * @var string
         */
        public $posts;

        /**
         * WordPress Terms table
         *
         * @since 2.3.0
         * @var string
         */
        public $terms;

        /**
         * WordPress Term Relationships table
         *
         * @since 2.3.0
         * @var string
         */
        public $term_relationships;

        /**
         * WordPress Term Taxonomy table
         *
         * @since 2.3.0
         * @var string
         */
        public $term_taxonomy;

        /**
         * WordPress Term Meta table.
         *
         * @since 4.4.0
         * @var string
         */
        public $termmeta;

        //
        // Global and Multisite tables
        //

        /**
         * WordPress User Metadata table
         *
         * @since 2.3.0
         * @var string
         */
        public $usermeta;

        /**
         * WordPress Users table
         *
         * @since 1.5.0
         * @var string
         */
        public $users;

        /**
         * Multisite Blogs table
         *
         * @since 3.0.0
         * @var string
         */
        public $blogs;

        /**
         * Multisite Blog Metadata table
         *
         * @since 5.1.0
         * @var string
         */
        public $blogmeta;

        /**
         * Multisite Registration Log table
         *
         * @since 3.0.0
         * @var string
         */
        public $registration_log;

        /**
         * Multisite Signups table
         *
         * @since 3.0.0
         * @var string
         */
        public $signups;

        /**
         * Multisite Sites table
         *
         * @since 3.0.0
         * @var string
         */
        public $site;

        /**
         * Multisite Sitewide Terms table
         *
         * @since 3.0.0
         * @var string
         */
        public $sitecategories;

        /**
         * Multisite Site Metadata table
         *
         * @since 3.0.0
         * @var string
         */
        public $sitemeta;

        /**
         * Format specifiers for DB columns. Columns not listed here default to %s. Initialized during WP load.
         *
         * Keys are column names, values are format types: 'ID' => '%d'
         *
         * @since 2.8.0
         * @see wpdb::prepare()
         * @see wpdb::insert()
         * @see wpdb::update()
         * @see wpdb::delete()
         * @see wp_set_wpdb_vars()
         * @var array
         */
        public $field_types = array();

        /**
         * Database table columns charset
         *
         * @since 2.2.0
         * @var string
         */
        public $charset;

        /**
         * Database table columns collate
         *
         * @since 2.2.0
         * @var string
         */
        public $collate;

        /**
         * Database Username
         *
         * @since 2.9.0
         * @var string
         */
        protected $dbuser;

        /**
         * Database Password
         *
         * @since 3.1.0
         * @var string
         */
        protected $dbpassword;

        /**
         * Database Name
         *
         * @since 3.1.0
         * @var string
         */
        protected $dbname;

        /**
         * Database Host
         *
         * @since 3.1.0
         * @var string
         */
        protected $dbhost;

        /**
         * Database Handle
         *
         * @since 0.71
         * @var string
         */
        protected $dbh;

        /**
         * A textual description of the last query/get_row/get_var call
         *
         * @since 3.0.0
         * @var string
         */
        public $func_call;

        /**
         * Whether MySQL is used as the database engine.
         *
         * Set in WPDB::db_connect() to true, by default. This is used when checking
         * against the required MySQL version for WordPress. Normally, a replacement
         * database drop-in (db.php) will skip these checks, but setting this to true
         * will force the checks to occur.
         *
         * @since 3.3.0
         * @var bool
         */
        public $is_mysql = null;

        /**
         * A list of incompatible SQL modes.
         *
         * @since 3.9.0
         * @var array
         */
        protected $incompatible_modes = array(
                'NO_ZERO_DATE',
                'ONLY_FULL_GROUP_BY',
                'STRICT_TRANS_TABLES',
                'STRICT_ALL_TABLES',
                'TRADITIONAL',
        );

        /**
         * Whether to use mysqli over mysql.
         *
         * @since 3.9.0
         * @var bool
         */
        private $use_mysqli = false;

        /**
         * Whether we've managed to successfully connect at some point
         *
         * @since 3.9.0
         * @var bool
         */
        private $has_connected = false;

        /**
         * Connects to the database server and selects a database
         *
         * PHP5 style constructor for compatibility with PHP5. Does
         * the actual setting up of the class properties and connection
         * to the database.
         *
         * @link https://core.trac.wordpress.org/ticket/3354
         * @since 2.0.8
         *
         * @global string $wp_version
         *
         * @param string $dbuser     MySQL database user
         * @param string $dbpassword MySQL database password
         * @param string $dbname     MySQL database name
         * @param string $dbhost     MySQL database host
         */
        public function __construct( $dbuser, $dbpassword, $dbname, $dbhost ) {
                register_shutdown_function( array( $this, '__destruct' ) );

                if ( WP_DEBUG && WP_DEBUG_DISPLAY ) {
                        $this->show_errors();
                }

                // Use ext/mysqli if it exists unless WP_USE_EXT_MYSQL is defined as true
                if ( function_exists( 'mysqli_connect' ) ) {
                        $this->use_mysqli = true;

                        if ( defined( 'WP_USE_EXT_MYSQL' ) ) {
                                $this->use_mysqli = ! WP_USE_EXT_MYSQL;
                        }
                }

                $this->dbuser     = $dbuser;
                $this->dbpassword = $dbpassword;
                $this->dbname     = $dbname;
                $this->dbhost     = $dbhost;

                // wp-config.php creation will manually connect when ready.
                if ( defined( 'WP_SETUP_CONFIG' ) ) {
                        return;
                }

                $this->db_connect();
        }

        /**
         * PHP5 style destructor and will run when database object is destroyed.
         *
         * @see wpdb::__construct()
         * @since 2.0.8
         * @return true
         */
        public function __destruct() {
                return true;
        }

        /**
         * Makes private properties readable for backward compatibility.
         *
         * @since 3.5.0
         *
         * @param string $name The private member to get, and optionally process
         * @return mixed The private member
         */
        public function __get( $name ) {
                if ( 'col_info' === $name ) {
                        $this->load_col_info();
                }

                return $this->$name;
        }

        /**
         * Makes private properties settable for backward compatibility.
         *
         * @since 3.5.0
         *
         * @param string $name  The private member to set
         * @param mixed  $value The value to set
         */
        public function __set( $name, $value ) {
                $protected_members = array(
                        'col_meta',
                        'table_charset',
                        'check_current_query',
                );
                if ( in_array( $name, $protected_members, true ) ) {
                        return;
                }
                $this->$name = $value;
        }

        /**
         * Makes private properties check-able for backward compatibility.
         *
         * @since 3.5.0
         *
         * @param string $name  The private member to check
         *
         * @return bool If the member is set or not
         */
        public function __isset( $name ) {
                return isset( $this->$name );
        }

        /**
         * Makes private properties un-settable for backward compatibility.
         *
         * @since 3.5.0
         *
         * @param string $name  The private member to unset
         */
        public function __unset( $name ) {
                unset( $this->$name );
        }

        /**
         * Set $this->charset and $this->collate
         *
         * @since 3.1.0
         */
        public function init_charset() {
                $charset = '';
                $collate = '';

                if ( function_exists( 'is_multisite' ) && is_multisite() ) {
                        $charset = 'utf8';
                        if ( defined( 'DB_COLLATE' ) && DB_COLLATE ) {
                                $collate = DB_COLLATE;
                        } else {
                                $collate = 'utf8_general_ci';
                        }
                } elseif ( defined( 'DB_COLLATE' ) ) {
                        $collate = DB_COLLATE;
                }

                if ( defined( 'DB_CHARSET' ) ) {
                        $charset = DB_CHARSET;
                }

                $charset_collate = $this->determine_charset( $charset, $collate );

                $this->charset = $charset_collate['charset'];
                $this->collate = $charset_collate['collate'];
        }

        /**
         * Determines the best charset and collation to use given a charset and collation.
         *
         * For example, when able, utf8mb4 should be used instead of utf8.
         *
         * @since 4.6.0
         *
         * @param string $charset The character set to check.
         * @param string $collate The collation to check.
         * @return array The most appropriate character set and collation to use.
         */
        public function determine_charset( $charset, $collate ) {
                if ( ( $this->use_mysqli && ! ( $this->dbh instanceof mysqli ) ) || empty( $this->dbh ) ) {
                        return compact( 'charset', 'collate' );
                }

                if ( 'utf8' === $charset && $this->has_cap( 'utf8mb4' ) ) {
                        $charset = 'utf8mb4';
                }

                if ( 'utf8mb4' === $charset && ! $this->has_cap( 'utf8mb4' ) ) {
                        $charset = 'utf8';
                        $collate = str_replace( 'utf8mb4_', 'utf8_', $collate );
                }

                if ( 'utf8mb4' === $charset ) {
                        // _general_ is outdated, so we can upgrade it to _unicode_, instead.
                        if ( ! $collate || 'utf8_general_ci' === $collate ) {
                                $collate = 'utf8mb4_unicode_ci';
                        } else {
                                $collate = str_replace( 'utf8_', 'utf8mb4_', $collate );
                        }
                }

                // _unicode_520_ is a better collation, we should use that when it's available.
                if ( $this->has_cap( 'utf8mb4_520' ) && 'utf8mb4_unicode_ci' === $collate ) {
                        $collate = 'utf8mb4_unicode_520_ci';
                }

                return compact( 'charset', 'collate' );
        }

        /**
         * Sets the connection's character set.
         *
         * @since 3.1.0
         *
         * @param resource $dbh     The resource given by mysql_connect
         * @param string   $charset Optional. The character set. Default null.
         * @param string   $collate Optional. The collation. Default null.
         */
        public function set_charset( $dbh, $charset = null, $collate = null ) {
                if ( ! isset( $charset ) ) {
                        $charset = $this->charset;
                }
                if ( ! isset( $collate ) ) {
                        $collate = $this->collate;
                }
                if ( $this->has_cap( 'collation' ) && ! empty( $charset ) ) {
                        $set_charset_succeeded = true;

                        if ( $this->use_mysqli ) {
                                if ( function_exists( 'mysqli_set_charset' ) && $this->has_cap( 'set_charset' ) ) {
                                        $set_charset_succeeded = mysqli_set_charset( $dbh, $charset );
                                }

                                if ( $set_charset_succeeded ) {
                                        $query = $this->prepare( 'SET NAMES %s', $charset );
                                        if ( ! empty( $collate ) ) {
                                                $query .= $this->prepare( ' COLLATE %s', $collate );
                                        }
                                        mysqli_query( $dbh, $query );
                                }
                        } else {
                                if ( function_exists( 'mysql_set_charset' ) && $this->has_cap( 'set_charset' ) ) {
                                        $set_charset_succeeded = mysql_set_charset( $charset, $dbh );
                                }
                                if ( $set_charset_succeeded ) {
                                        $query = $this->prepare( 'SET NAMES %s', $charset );
                                        if ( ! empty( $collate ) ) {
                                                $query .= $this->prepare( ' COLLATE %s', $collate );
                                        }
                                        mysql_query( $query, $dbh );
                                }
                        }
                }
        }

        /**
         * Change the current SQL mode, and ensure its WordPress compatibility.
         *
         * If no modes are passed, it will ensure the current MySQL server
         * modes are compatible.
         *
         * @since 3.9.0
         *
         * @param array $modes Optional. A list of SQL modes to set.
         */
        public function set_sql_mode( $modes = array() ) {
                if ( empty( $modes ) ) {
                        if ( $this->use_mysqli ) {
                                $res = mysqli_query( $this->dbh, 'SELECT @@SESSION.sql_mode' );
                        } else {
                                $res = mysql_query( 'SELECT @@SESSION.sql_mode', $this->dbh );
                        }

                        if ( empty( $res ) ) {
                                return;
                        }

                        if ( $this->use_mysqli ) {
                                $modes_array = mysqli_fetch_array( $res );
                                if ( empty( $modes_array[0] ) ) {
                                        return;
                                }
                                $modes_str = $modes_array[0];
                        } else {
                                $modes_str = mysql_result( $res, 0 );
                        }

                        if ( empty( $modes_str ) ) {
                                return;
                        }

                        $modes = explode( ',', $modes_str );
                }

                $modes = array_change_key_case( $modes, CASE_UPPER );

                /**
                 * Filters the list of incompatible SQL modes to exclude.
                 *
                 * @since 3.9.0
                 *
                 * @param array $incompatible_modes An array of incompatible modes.
                 */
                $incompatible_modes = (array) apply_filters( 'incompatible_sql_modes', $this->incompatible_modes );

                foreach ( $modes as $i => $mode ) {
                        if ( in_array( $mode, $incompatible_modes ) ) {
                                unset( $modes[ $i ] );
                        }
                }

                $modes_str = implode( ',', $modes );

                if ( $this->use_mysqli ) {
                        mysqli_query( $this->dbh, "SET SESSION sql_mode='$modes_str'" );
                } else {
                        mysql_query( "SET SESSION sql_mode='$modes_str'", $this->dbh );
                }
        }

        /**
         * Sets the table prefix for the WordPress tables.
         *
         * @since 2.5.0
         *
         * @param string $prefix          Alphanumeric name for the new prefix.
         * @param bool   $set_table_names Optional. Whether the table names, e.g. wpdb::$posts, should be updated or not.
         * @return string|WP_Error Old prefix or WP_Error on error
         */
        public function set_prefix( $prefix, $set_table_names = true ) {

                if ( preg_match( '|[^a-z0-9_]|i', $prefix ) ) {
                        return new WP_Error( 'invalid_db_prefix', 'Invalid database prefix' );
                }

                $old_prefix = is_multisite() ? '' : $prefix;

                if ( isset( $this->base_prefix ) ) {
                        $old_prefix = $this->base_prefix;
                }

                $this->base_prefix = $prefix;

                if ( $set_table_names ) {
                        foreach ( $this->tables( 'global' ) as $table => $prefixed_table ) {
                                $this->$table = $prefixed_table;
                        }

                        if ( is_multisite() && empty( $this->blogid ) ) {
                                return $old_prefix;
                        }

                        $this->prefix = $this->get_blog_prefix();

                        foreach ( $this->tables( 'blog' ) as $table => $prefixed_table ) {
                                $this->$table = $prefixed_table;
                        }

                        foreach ( $this->tables( 'old' ) as $table => $prefixed_table ) {
                                $this->$table = $prefixed_table;
                        }
                }
                return $old_prefix;
        }

        /**
         * Sets blog id.
         *
         * @since 3.0.0
         *
         * @param int $blog_id
         * @param int $network_id Optional.
         * @return int previous blog id
         */
        public function set_blog_id( $blog_id, $network_id = 0 ) {
                if ( ! empty( $network_id ) ) {
                        $this->siteid = $network_id;
                }

                $old_blog_id  = $this->blogid;
                $this->blogid = $blog_id;

                $this->prefix = $this->get_blog_prefix();

                foreach ( $this->tables( 'blog' ) as $table => $prefixed_table ) {
                        $this->$table = $prefixed_table;
                }

                foreach ( $this->tables( 'old' ) as $table => $prefixed_table ) {
                        $this->$table = $prefixed_table;
                }

                return $old_blog_id;
        }

        /**
         * Gets blog prefix.
         *
         * @since 3.0.0
         * @param int $blog_id Optional.
         * @return string Blog prefix.
         */
        public function get_blog_prefix( $blog_id = null ) {
                if ( is_multisite() ) {
                        if ( null === $blog_id ) {
                                $blog_id = $this->blogid;
                        }
                        $blog_id = (int) $blog_id;
                        if ( defined( 'MULTISITE' ) && ( 0 == $blog_id || 1 == $blog_id ) ) {
                                return $this->base_prefix;
                        } else {
                                return $this->base_prefix . $blog_id . '_';
                        }
                } else {
                        return $this->base_prefix;
                }
        }

        /**
         * Returns an array of WordPress tables.
         *
         * Also allows for the CUSTOM_USER_TABLE and CUSTOM_USER_META_TABLE to
         * override the WordPress users and usermeta tables that would otherwise
         * be determined by the prefix.
         *
         * The scope argument can take one of the following:
         *
         * 'all' - returns 'all' and 'global' tables. No old tables are returned.
         * 'blog' - returns the blog-level tables for the queried blog.
         * 'global' - returns the global tables for the installation, returning multisite tables only if running multisite.
         * 'ms_global' - returns the multisite global tables, regardless if current installation is multisite.
         * 'old' - returns tables which are deprecated.
         *
         * @since 3.0.0
         * @uses wpdb::$tables
         * @uses wpdb::$old_tables
         * @uses wpdb::$global_tables
         * @uses wpdb::$ms_global_tables
         *
         * @param string $scope   Optional. Can be all, global, ms_global, blog, or old tables. Defaults to all.
         * @param bool   $prefix  Optional. Whether to include table prefixes. Default true. If blog
         *                        prefix is requested, then the custom users and usermeta tables will be mapped.
         * @param int    $blog_id Optional. The blog_id to prefix. Defaults to wpdb::$blogid. Used only when prefix is requested.
         * @return array Table names. When a prefix is requested, the key is the unprefixed table name.
         */
        public function tables( $scope = 'all', $prefix = true, $blog_id = 0 ) {
                switch ( $scope ) {
                        case 'all':
                                $tables = array_merge( $this->global_tables, $this->tables );
                                if ( is_multisite() ) {
                                        $tables = array_merge( $tables, $this->ms_global_tables );
                                }
                                break;
                        case 'blog':
                                $tables = $this->tables;
                                break;
                        case 'global':
                                $tables = $this->global_tables;
                                if ( is_multisite() ) {
                                        $tables = array_merge( $tables, $this->ms_global_tables );
                                }
                                break;
                        case 'ms_global':
                                $tables = $this->ms_global_tables;
                                break;
                        case 'old':
                                $tables = $this->old_tables;
                                break;
                        default:
                                return array();
                }

                if ( $prefix ) {
                        if ( ! $blog_id ) {
                                $blog_id = $this->blogid;
                        }
                        $blog_prefix   = $this->get_blog_prefix( $blog_id );
                        $base_prefix   = $this->base_prefix;
                        $global_tables = array_merge( $this->global_tables, $this->ms_global_tables );
                        foreach ( $tables as $k => $table ) {
                                if ( in_array( $table, $global_tables ) ) {
                                        $tables[ $table ] = $base_prefix . $table;
                                } else {
                                        $tables[ $table ] = $blog_prefix . $table;
                                }
                                unset( $tables[ $k ] );
                        }

                        if ( isset( $tables['users'] ) && defined( 'CUSTOM_USER_TABLE' ) ) {
                                $tables['users'] = CUSTOM_USER_TABLE;
                        }

                        if ( isset( $tables['usermeta'] ) && defined( 'CUSTOM_USER_META_TABLE' ) ) {
                                $tables['usermeta'] = CUSTOM_USER_META_TABLE;
                        }
                }

                return $tables;
        }

        /**
         * Selects a database using the current database connection.
         *
         * The database name will be changed based on the current database
         * connection. On failure, the execution will bail and display an DB error.
         *
         * @since 0.71
         *
         * @param string        $db  MySQL database name
         * @param resource|null $dbh Optional link identifier.
         */
        public function select( $db, $dbh = null ) {
                if ( is_null( $dbh ) ) {
                        $dbh = $this->dbh;
                }

                if ( $this->use_mysqli ) {
                        $success = mysqli_select_db( $dbh, $db );
                } else {
                        $success = mysql_select_db( $db, $dbh );
                }
                if ( ! $success ) {
                        $this->ready = false;
                        if ( ! did_action( 'template_redirect' ) ) {
                                wp_load_translations_early();

                                $message = '<h1>' . __( 'Can&#8217;t select database' ) . "</h1>\n";

                                $message .= '<p>' . sprintf(
                                        /* translators: %s: Database name. */
                                        __( 'We were able to connect to the database server (which means your username and password is okay) but not able to select the %s database.' ),
                                        '<code>' . htmlspecialchars( $db, ENT_QUOTES ) . '</code>'
                                ) . "</p>\n";

                                $message .= "<ul>\n";
                                $message .= '<li>' . __( 'Are you sure it exists?' ) . "</li>\n";

                                $message .= '<li>' . sprintf(
                                        /* translators: 1: Database user, 2: Database name. */
                                        __( 'Does the user %1$s have permission to use the %2$s database?' ),
                                        '<code>' . htmlspecialchars( $this->dbuser, ENT_QUOTES ) . '</code>',
                                        '<code>' . htmlspecialchars( $db, ENT_QUOTES ) . '</code>'
                                ) . "</li>\n";

                                $message .= '<li>' . sprintf(
                                        /* translators: %s: Database name. */
                                        __( 'On some systems the name of your database is prefixed with your username, so it would be like <code>username_%1$s</code>. Could that be the problem?' ),
                                        htmlspecialchars( $db, ENT_QUOTES )
                                ) . "</li>\n";

                                $message .= "</ul>\n";

                                $message .= '<p>' . sprintf(
                                        /* translators: %s: Support forums URL. */
                                        __( 'If you don&#8217;t know how to set up a database you should <strong>contact your host</strong>. If all else fails you may find help at the <a href="%s">WordPress Support Forums</a>.' ),
                                        __( 'https://wordpress.org/support/forums/' )
                                ) . "</p>\n";

                                $this->bail( $message, 'db_select_fail' );
                        }
                }
        }

        /**
         * Do not use, deprecated.
         *
         * Use esc_sql() or wpdb::prepare() instead.
         *
         * @since 2.8.0
         * @deprecated 3.6.0 Use wpdb::prepare()
         * @see wpdb::prepare
         * @see esc_sql()
         *
         * @param string $string
         * @return string
         */
        function _weak_escape( $string ) {
                if ( func_num_args() === 1 && function_exists( '_deprecated_function' ) ) {
                        _deprecated_function( __METHOD__, '3.6.0', 'wpdb::prepare() or esc_sql()' );
                }
                return addslashes( $string );
        }

        /**
         * Real escape, using mysqli_real_escape_string() or mysql_real_escape_string()
         *
         * @see mysqli_real_escape_string()
         * @see mysql_real_escape_string()
         * @since 2.8.0
         *
         * @param  string $string to escape
         * @return string escaped
         */
        function _real_escape( $string ) {
                if ( $this->dbh ) {
                        if ( $this->use_mysqli ) {
                                $escaped = mysqli_real_escape_string( $this->dbh, $string );
                        } else {
                                $escaped = mysql_real_escape_string( $string, $this->dbh );
                        }
                } else {
                        $class = get_class( $this );
                        if ( function_exists( '__' ) ) {
                                /* translators: %s: Database access abstraction class, usually wpdb or a class extending wpdb. */
                                _doing_it_wrong( $class, sprintf( __( '%s must set a database connection for use with escaping.' ), $class ), '3.6.0' );
                        } else {
                                _doing_it_wrong( $class, sprintf( '%s must set a database connection for use with escaping.', $class ), '3.6.0' );
                        }
                        $escaped = addslashes( $string );
                }

                return $this->add_placeholder_escape( $escaped );
        }

        /**
         * Escape data. Works on arrays.
         *
         * @uses wpdb::_real_escape()
         * @since  2.8.0
         *
         * @param  string|array $data
         * @return string|array escaped
         */
        public function _escape( $data ) {
                if ( is_array( $data ) ) {
                        foreach ( $data as $k => $v ) {
                                if ( is_array( $v ) ) {
                                        $data[ $k ] = $this->_escape( $v );
                                } else {
                                        $data[ $k ] = $this->_real_escape( $v );
                                }
                        }
                } else {
                        $data = $this->_real_escape( $data );
                }

                return $data;
        }

        /**
         * Do not use, deprecated.
         *
         * Use esc_sql() or wpdb::prepare() instead.
         *
         * @since 0.71
         * @deprecated 3.6.0 Use wpdb::prepare()
         * @see wpdb::prepare()
         * @see esc_sql()
         *
         * @param mixed $data
         * @return mixed
         */
        public function escape( $data ) {
                if ( func_num_args() === 1 && function_exists( '_deprecated_function' ) ) {
                        _deprecated_function( __METHOD__, '3.6.0', 'wpdb::prepare() or esc_sql()' );
                }
                if ( is_array( $data ) ) {
                        foreach ( $data as $k => $v ) {
                                if ( is_array( $v ) ) {
                                        $data[ $k ] = $this->escape( $v, 'recursive' );
                                } else {
                                        $data[ $k ] = $this->_weak_escape( $v, 'internal' );
                                }
                        }
                } else {
                        $data = $this->_weak_escape( $data, 'internal' );
                }

                return $data;
        }

        /**
         * Escapes content by reference for insertion into the database, for security
         *
         * @uses wpdb::_real_escape()
         *
         * @since 2.3.0
         *
         * @param string $string to escape
         */
        public function escape_by_ref( &$string ) {
                if ( ! is_float( $string ) ) {
                        $string = $this->_real_escape( $string );
                }
        }

        /**
         * Prepares a SQL query for safe execution. Uses sprintf()-like syntax.
         *
         * The following placeholders can be used in the query string:
         *   %d (integer)
         *   %f (float)
         *   %s (string)
         *
         * All placeholders MUST be left unquoted in the query string. A corresponding argument
         * MUST be passed for each placeholder.
         *
         * For compatibility with old behavior, numbered or formatted string placeholders (eg, %1$s, %5s)
         * will not have quotes added by this function, so should be passed with appropriate quotes around
         * them for your usage.
         *
         * Literal percentage signs (%) in the query string must be written as %%. Percentage wildcards (for example,
         * to use in LIKE syntax) must be passed via a substitution argument containing the complete LIKE string, these
         * cannot be inserted directly in the query string. Also see wpdb::esc_like().
         *
         * Arguments may be passed as individual arguments to the method, or as a single array containing
         * all arguments. A combination of the two is not supported.
         *
         * Examples:
         *     $wpdb->prepare( "SELECT * FROM `table` WHERE `column` = %s AND `field` = %d OR `other_field` LIKE %s", array( 'foo', 1337, '%bar' ) );
         *     $wpdb->prepare( "SELECT DATE_FORMAT(`field`, '%%c') FROM `table` WHERE `column` = %s", 'foo' );
         *
         * @link https://secure.php.net/sprintf Description of syntax.
         * @since 2.3.0
         * @since 5.3.0 Formalized the existing and already documented `...$args` parameter
         *              by updating the function signature. The second parameter was changed
         *              from `$args` to `...$args`.
         *
         * @param string      $query   Query statement with sprintf()-like placeholders
         * @param array|mixed $args    The array of variables to substitute into the query's placeholders
         *                             if being called with an array of arguments, or the first variable
         *                             to substitute into the query's placeholders if being called with
         *                             individual arguments.
         * @param mixed       ...$args Further variables to substitute into the query's placeholders
         *                             if being called with individual arguments.
         * @return string|void Sanitized query string, if there is a query to prepare.
         */
        public function prepare( $query, ...$args ) {
                if ( is_null( $query ) ) {
                        return;
                }

                // This is not meant to be foolproof -- but it will catch obviously incorrect usage.
                if ( strpos( $query, '%' ) === false ) {
                        wp_load_translations_early();
                        _doing_it_wrong(
                                'wpdb::prepare',
                                sprintf(
                                        /* translators: %s: wpdb::prepare() */
                                        __( 'The query argument of %s must have a placeholder.' ),
                                        'wpdb::prepare()'
                                ),
                                '3.9.0'
                        );
                }

                // If args were passed as an array (as in vsprintf), move them up.
                $passed_as_array = false;
                if ( is_array( $args[0] ) && count( $args ) == 1 ) {
                        $passed_as_array = true;
                        $args            = $args[0];
                }

                foreach ( $args as $arg ) {
                        if ( ! is_scalar( $arg ) && ! is_null( $arg ) ) {
                                wp_load_translations_early();
                                _doing_it_wrong(
                                        'wpdb::prepare',
                                        sprintf(
                                                /* translators: %s: Value type. */
                                                __( 'Unsupported value type (%s).' ),
                                                gettype( $arg )
                                        ),
                                        '4.8.2'
                                );
                        }
                }

                /*
                 * Specify the formatting allowed in a placeholder. The following are allowed:
                 *
                 * - Sign specifier. eg, $+d
                 * - Numbered placeholders. eg, %1$s
                 * - Padding specifier, including custom padding characters. eg, %05s, %'#5s
                 * - Alignment specifier. eg, %05-s
                 * - Precision specifier. eg, %.2f
                 */
                $allowed_format = '(?:[1-9][0-9]*[$])?[-+0-9]*(?: |0|\'.)?[-+0-9]*(?:\.[0-9]+)?';

                /*
                 * If a %s placeholder already has quotes around it, removing the existing quotes and re-inserting them
                 * ensures the quotes are consistent.
                 *
                 * For backward compatibility, this is only applied to %s, and not to placeholders like %1$s, which are frequently
                 * used in the middle of longer strings, or as table name placeholders.
                 */
                $query = str_replace( "'%s'", '%s', $query ); // Strip any existing single quotes.
                $query = str_replace( '"%s"', '%s', $query ); // Strip any existing double quotes.
                $query = preg_replace( '/(?<!%)%s/', "'%s'", $query ); // Quote the strings, avoiding escaped strings like %%s.

                $query = preg_replace( "/(?<!%)(%($allowed_format)?f)/", '%\\2F', $query ); // Force floats to be locale unaware.

                $query = preg_replace( "/%(?:%|$|(?!($allowed_format)?[sdF]))/", '%%\\1', $query ); // Escape any unescaped percents.

                // Count the number of valid placeholders in the query.
                $placeholders = preg_match_all( "/(^|[^%]|(%%)+)%($allowed_format)?[sdF]/", $query, $matches );

                if ( count( $args ) !== $placeholders ) {
                        if ( 1 === $placeholders && $passed_as_array ) {
                                // If the passed query only expected one argument, but the wrong number of arguments were sent as an array, bail.
                                wp_load_translations_early();
                                _doing_it_wrong(
                                        'wpdb::prepare',
                                        __( 'The query only expected one placeholder, but an array of multiple placeholders was sent.' ),
                                        '4.9.0'
                                );

                                return;
                        } else {
                                /*
                                 * If we don't have the right number of placeholders, but they were passed as individual arguments,
                                 * or we were expecting multiple arguments in an array, throw a warning.
                                 */
                                wp_load_translations_early();
                                _doing_it_wrong(
                                        'wpdb::prepare',
                                        sprintf(
                                                /* translators: 1: Number of placeholders, 2: Number of arguments passed. */
                                                __( 'The query does not contain the correct number of placeholders (%1$d) for the number of arguments passed (%2$d).' ),
                                                $placeholders,
                                                count( $args )
                                        ),
                                        '4.8.3'
                                );
                        }
                }

                array_walk( $args, array( $this, 'escape_by_ref' ) );
                $query = vsprintf( $query, $args );

                return $this->add_placeholder_escape( $query );
        }

        /**
         * First half of escaping for LIKE special characters % and _ before preparing for MySQL.
         *
         * Use this only before wpdb::prepare() or esc_sql().  Reversing the order is very bad for security.
         *
         * Example Prepared Statement:
         *
         *     $wild = '%';
         *     $find = 'only 43% of planets';
         *     $like = $wild . $wpdb->esc_like( $find ) . $wild;
         *     $sql  = $wpdb->prepare( "SELECT * FROM $wpdb->posts WHERE post_content LIKE %s", $like );
         *
         * Example Escape Chain:
         *
         *     $sql  = esc_sql( $wpdb->esc_like( $input ) );
         *
         * @since 4.0.0
         *
         * @param string $text The raw text to be escaped. The input typed by the user should have no
         *                     extra or deleted slashes.
         * @return string Text in the form of a LIKE phrase. The output is not SQL safe. Call $wpdb::prepare()
         *                or real_escape next.
         */
        public function esc_like( $text ) {
                return addcslashes( $text, '_%\\' );
        }

        /**
         * Print SQL/DB error.
         *
         * @since 0.71
         * @global array $EZSQL_ERROR Stores error information of query and error string
         *
         * @param string $str The error to display
         * @return false|void False if the showing of errors is disabled.
         */
        public function print_error( $str = '' ) {
                global $EZSQL_ERROR;

                if ( ! $str ) {
                        if ( $this->use_mysqli ) {
                                $str = mysqli_error( $this->dbh );
                        } else {
                                $str = mysql_error( $this->dbh );
                        }
                }
                $EZSQL_ERROR[] = array(
                        'query'     => $this->last_query,
                        'error_str' => $str,
                );

                if ( $this->suppress_errors ) {
                        return false;
                }

                wp_load_translations_early();

                $caller = $this->get_caller();
                if ( $caller ) {
                        /* translators: 1: Database error message, 2: SQL query, 3: Name of the calling function. */
                        $error_str = sprintf( __( 'WordPress database error %1$s for query %2$s made by %3$s' ), $str, $this->last_query, $caller );
                } else {
                        /* translators: 1: Database error message, 2: SQL query. */
                        $error_str = sprintf( __( 'WordPress database error %1$s for query %2$s' ), $str, $this->last_query );
                }

                error_log( $error_str );

                // Are we showing errors?
                if ( ! $this->show_errors ) {
                        return false;
                }

                // If there is an error then take note of it
                if ( is_multisite() ) {
                        $msg = sprintf(
                                "%s [%s]\n%s\n",
                                __( 'WordPress database error:' ),
                                $str,
                                $this->last_query
                        );

                        if ( defined( 'ERRORLOGFILE' ) ) {
                                error_log( $msg, 3, ERRORLOGFILE );
                        }
                        if ( defined( 'DIEONDBERROR' ) ) {
                                wp_die( $msg );
                        }
                } else {
                        $str   = htmlspecialchars( $str, ENT_QUOTES );
                        $query = htmlspecialchars( $this->last_query, ENT_QUOTES );

                        printf(
                                '<div id="error"><p class="wpdberror"><strong>%s</strong> [%s]<br /><code>%s</code></p></div>',
                                __( 'WordPress database error:' ),
                                $str,
                                $query
                        );
                }
        }

        /**
         * Enables showing of database errors.
         *
         * This function should be used only to enable showing of errors.
         * wpdb::hide_errors() should be used instead for hiding of errors. However,
         * this function can be used to enable and disable showing of database
         * errors.
         *
         * @since 0.71
         * @see wpdb::hide_errors()
         *
         * @param bool $show Whether to show or hide errors
         * @return bool Old value for showing errors.
         */
        public function show_errors( $show = true ) {
                $errors            = $this->show_errors;
                $this->show_errors = $show;
                return $errors;
        }

        /**
         * Disables showing of database errors.
         *
         * By default database errors are not shown.
         *
         * @since 0.71
         * @see wpdb::show_errors()
         *
         * @return bool Whether showing of errors was active
         */
        public function hide_errors() {
                $show              = $this->show_errors;
                $this->show_errors = false;
                return $show;
        }

        /**
         * Whether to suppress database errors.
         *
         * By default database errors are suppressed, with a simple
         * call to this function they can be enabled.
         *
         * @since 2.5.0
         * @see wpdb::hide_errors()
         * @param bool $suppress Optional. New value. Defaults to true.
         * @return bool Old value
         */
        public function suppress_errors( $suppress = true ) {
                $errors                = $this->suppress_errors;
                $this->suppress_errors = (bool) $suppress;
                return $errors;
        }

        /**
         * Kill cached query results.
         *
         * @since 0.71
         */
        public function flush() {
                $this->last_result   = array();
                $this->col_info      = null;
                $this->last_query    = null;
                $this->rows_affected = 0;
                $this->num_rows      = 0;
                $this->last_error    = '';

                if ( $this->use_mysqli && $this->result instanceof mysqli_result ) {
                        mysqli_free_result( $this->result );
                        $this->result = null;

                        // Sanity check before using the handle
                        if ( empty( $this->dbh ) || ! ( $this->dbh instanceof mysqli ) ) {
                                return;
                        }

                        // Clear out any results from a multi-query
                        while ( mysqli_more_results( $this->dbh ) ) {
                                mysqli_next_result( $this->dbh );
                        }
                } elseif ( is_resource( $this->result ) ) {
                        mysql_free_result( $this->result );
                }
        }

        /**
         * Connect to and select database.
         *
         * If $allow_bail is false, the lack of database connection will need
         * to be handled manually.
         *
         * @since 3.0.0
         * @since 3.9.0 $allow_bail parameter added.
         *
         * @param bool $allow_bail Optional. Allows the function to bail. Default true.
         * @return bool True with a successful connection, false on failure.
         */
        public function db_connect( $allow_bail = true ) {
                $this->is_mysql = true;

                /*
                 * Deprecated in 3.9+ when using MySQLi. No equivalent
                 * $new_link parameter exists for mysqli_* functions.
                 */
                $new_link     = defined( 'MYSQL_NEW_LINK' ) ? MYSQL_NEW_LINK : true;
                $client_flags = defined( 'MYSQL_CLIENT_FLAGS' ) ? MYSQL_CLIENT_FLAGS : 0;

                if ( $this->use_mysqli ) {
                        $this->dbh = mysqli_init();

                        $host    = $this->dbhost;
                        $port    = null;
                        $socket  = null;
                        $is_ipv6 = false;

                        $host_data = $this->parse_db_host( $this->dbhost );
                        if ( $host_data ) {
                                list( $host, $port, $socket, $is_ipv6 ) = $host_data;
                        }

                        /*
                         * If using the `mysqlnd` library, the IPv6 address needs to be
                         * enclosed in square brackets, whereas it doesn't while using the
                         * `libmysqlclient` library.
                         * @see https://bugs.php.net/bug.php?id=67563
                         */
                        if ( $is_ipv6 && extension_loaded( 'mysqlnd' ) ) {
                                $host = "[$host]";
                        }

                        if ( WP_DEBUG ) {
                                mysqli_real_connect( $this->dbh, $host, $this->dbuser, $this->dbpassword, null, $port, $socket, $client_flags );
                        } else {
                                // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
                                @mysqli_real_connect( $this->dbh, $host, $this->dbuser, $this->dbpassword, null, $port, $socket, $client_flags );
                        }

                        if ( $this->dbh->connect_errno ) {
                                $this->dbh = null;

                                /*
                                 * It's possible ext/mysqli is misconfigured. Fall back to ext/mysql if:
                                 *  - We haven't previously connected, and
                                 *  - WP_USE_EXT_MYSQL isn't set to false, and
                                 *  - ext/mysql is loaded.
                                 */
                                $attempt_fallback = true;

                                if ( $this->has_connected ) {
                                        $attempt_fallback = false;
                                } elseif ( defined( 'WP_USE_EXT_MYSQL' ) && ! WP_USE_EXT_MYSQL ) {
                                        $attempt_fallback = false;
                                } elseif ( ! function_exists( 'mysql_connect' ) ) {
                                        $attempt_fallback = false;
                                }

                                if ( $attempt_fallback ) {
                                        $this->use_mysqli = false;
                                        return $this->db_connect( $allow_bail );
                                }
                        }
                } else {
                        if ( WP_DEBUG ) {
                                $this->dbh = mysql_connect( $this->dbhost, $this->dbuser, $this->dbpassword, $new_link, $client_flags );
                        } else {
                                // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
                                $this->dbh = @mysql_connect( $this->dbhost, $this->dbuser, $this->dbpassword, $new_link, $client_flags );
                        }
                }

                if ( ! $this->dbh && $allow_bail ) {
                        wp_load_translations_early();

                        // Load custom DB error template, if present.
                        if ( file_exists( WP_CONTENT_DIR . '/db-error.php' ) ) {
                                require_once( WP_CONTENT_DIR . '/db-error.php' );
                                die();
                        }

                        $message = '<h1>' . __( 'Error establishing a database connection' ) . "</h1>\n";

                        $message .= '<p>' . sprintf(
                                /* translators: 1: wp-config.php, 2: Database host. */
                                __( 'This either means that the username and password information in your %1$s file is incorrect or we can&#8217;t contact the database server at %2$s. This could mean your host&#8217;s database server is down.' ),
                                '<code>wp-config.php</code>',
                                '<code>' . htmlspecialchars( $this->dbhost, ENT_QUOTES ) . '</code>'
                        ) . "</p>\n";

                        $message .= "<ul>\n";
                        $message .= '<li>' . __( 'Are you sure you have the correct username and password?' ) . "</li>\n";
                        $message .= '<li>' . __( 'Are you sure you have typed the correct hostname?' ) . "</li>\n";
                        $message .= '<li>' . __( 'Are you sure the database server is running?' ) . "</li>\n";
                        $message .= "</ul>\n";

                        $message .= '<p>' . sprintf(
                                /* translators: %s: Support forums URL. */
                                __( 'If you&#8217;re unsure what these terms mean you should probably contact your host. If you still need help you can always visit the <a href="%s">WordPress Support Forums</a>.' ),
                                __( 'https://wordpress.org/support/forums/' )
                        ) . "</p>\n";

                        $this->bail( $message, 'db_connect_fail' );

                        return false;
                } elseif ( $this->dbh ) {
                        if ( ! $this->has_connected ) {
                                $this->init_charset();
                        }

                        $this->has_connected = true;

                        $this->set_charset( $this->dbh );

                        $this->ready = true;
                        $this->set_sql_mode();
                        $this->select( $this->dbname, $this->dbh );

                        return true;
                }

                return false;
        }

        /**
         * Parse the DB_HOST setting to interpret it for mysqli_real_connect.
         *
         * mysqli_real_connect doesn't support the host param including a port or
         * socket like mysql_connect does. This duplicates how mysql_connect detects
         * a port and/or socket file.
         *
         * @since 4.9.0
         *
         * @param string $host The DB_HOST setting to parse.
         * @return array|bool Array containing the host, the port, the socket and whether
         *                    it is an IPv6 address, in that order. If $host couldn't be parsed,
         *                    returns false.
         */
        public function parse_db_host( $host ) {
                $port    = null;
                $socket  = null;
                $is_ipv6 = false;

                // First peel off the socket parameter from the right, if it exists.
                $socket_pos = strpos( $host, ':/' );
                if ( $socket_pos !== false ) {
                        $socket = substr( $host, $socket_pos + 1 );
                        $host   = substr( $host, 0, $socket_pos );
                }

                // We need to check for an IPv6 address first.
                // An IPv6 address will always contain at least two colons.
                if ( substr_count( $host, ':' ) > 1 ) {
                        $pattern = '#^(?:\[)?(?P<host>[0-9a-fA-F:]+)(?:\]:(?P<port>[\d]+))?#';
                        $is_ipv6 = true;
                } else {
                        // We seem to be dealing with an IPv4 address.
                        $pattern = '#^(?P<host>[^:/]*)(?::(?P<port>[\d]+))?#';
                }

                $matches = array();
                $result  = preg_match( $pattern, $host, $matches );

                if ( 1 !== $result ) {
                        // Couldn't parse the address, bail.
                        return false;
                }

                $host = '';
                foreach ( array( 'host', 'port' ) as $component ) {
                        if ( ! empty( $matches[ $component ] ) ) {
                                $$component = $matches[ $component ];
                        }
                }

                return array( $host, $port, $socket, $is_ipv6 );
        }

        /**
         * Checks that the connection to the database is still up. If not, try to reconnect.
         *
         * If this function is unable to reconnect, it will forcibly die, or if after the
         * the {@see 'template_redirect'} hook has been fired, return false instead.
         *
         * If $allow_bail is false, the lack of database connection will need
         * to be handled manually.
         *
         * @since 3.9.0
         *
         * @param bool $allow_bail Optional. Allows the function to bail. Default true.
         * @return bool|void True if the connection is up.
         */
        public function check_connection( $allow_bail = true ) {
                if ( $this->use_mysqli ) {
                        if ( ! empty( $this->dbh ) && mysqli_ping( $this->dbh ) ) {
                                return true;
                        }
                } else {
                        if ( ! empty( $this->dbh ) && mysql_ping( $this->dbh ) ) {
                                return true;
                        }
                }

                $error_reporting = false;

                // Disable warnings, as we don't want to see a multitude of "unable to connect" messages
                if ( WP_DEBUG ) {
                        $error_reporting = error_reporting();
                        error_reporting( $error_reporting & ~E_WARNING );
                }

                for ( $tries = 1; $tries <= $this->reconnect_retries; $tries++ ) {
                        // On the last try, re-enable warnings. We want to see a single instance of the
                        // "unable to connect" message on the bail() screen, if it appears.
                        if ( $this->reconnect_retries === $tries && WP_DEBUG ) {
                                error_reporting( $error_reporting );
                        }

                        if ( $this->db_connect( false ) ) {
                                if ( $error_reporting ) {
                                        error_reporting( $error_reporting );
                                }

                                return true;
                        }

                        sleep( 1 );
                }

                // If template_redirect has already happened, it's too late for wp_die()/dead_db().
                // Let's just return and hope for the best.
                if ( did_action( 'template_redirect' ) ) {
                        return false;
                }

                if ( ! $allow_bail ) {
                        return false;
                }

                wp_load_translations_early();

                $message = '<h1>' . __( 'Error reconnecting to the database' ) . "</h1>\n";

                $message .= '<p>' . sprintf(
                        /* translators: %s: Database host. */
                        __( 'This means that we lost contact with the database server at %s. This could mean your host&#8217;s database server is down.' ),
                        '<code>' . htmlspecialchars( $this->dbhost, ENT_QUOTES ) . '</code>'
                ) . "</p>\n";

                $message .= "<ul>\n";
                $message .= '<li>' . __( 'Are you sure the database server is running?' ) . "</li>\n";
                $message .= '<li>' . __( 'Are you sure the database server is not under particularly heavy load?' ) . "</li>\n";
                $message .= "</ul>\n";

                $message .= '<p>' . sprintf(
                        /* translators: %s: Support forums URL. */
                        __( 'If you&#8217;re unsure what these terms mean you should probably contact your host. If you still need help you can always visit the <a href="%s">WordPress Support Forums</a>.' ),
                        __( 'https://wordpress.org/support/forums/' )
                ) . "</p>\n";

                // We weren't able to reconnect, so we better bail.
                $this->bail( $message, 'db_connect_fail' );

                // Call dead_db() if bail didn't die, because this database is no more. It has ceased to be (at least temporarily).
                dead_db();
        }

        /**
         * Perform a MySQL database query, using current database connection.
         *
         * More information can be found on the codex page.
         *
         * @since 0.71
         *
         * @param string $query Database query
         * @return int|bool Boolean true for CREATE, ALTER, TRUNCATE and DROP queries. Number of rows
         *                  affected/selected for all other queries. Boolean false on error.
         */
        public function query( $query ) {
                if ( ! $this->ready ) {
                        $this->check_current_query = true;
                        return false;
                }

                /**
                 * Filters the database query.
                 *
                 * Some queries are made before the plugins have been loaded,
                 * and thus cannot be filtered with this method.
                 *
                 * @since 2.1.0
                 *
                 * @param string $query Database query.
                 */
                 if(!$this->suppress_filters)   $query = apply_filters( 'query', $query );

                $this->flush();

                // Log how the function was called
                $this->func_call = "\$db->query(\"$query\")";

                // If we're writing to the database, make sure the query will write safely.
                if ( $this->check_current_query && ! $this->check_ascii( $query ) ) {
                        $stripped_query = $this->strip_invalid_text_from_query( $query );
                        // strip_invalid_text_from_query() can perform queries, so we need
                        // to flush again, just to make sure everything is clear.
                        $this->flush();
                        if ( $stripped_query !== $query ) {
                                $this->insert_id = 0;
                                return false;
                        }
                }

                $this->check_current_query = true;

                // Keep track of the last query for debug.
                $this->last_query = $query;

                $this->_do_query( $query );

                // MySQL server has gone away, try to reconnect.
                $mysql_errno = 0;
                if ( ! empty( $this->dbh ) ) {
                        if ( $this->use_mysqli ) {
                                if ( $this->dbh instanceof mysqli ) {
                                        $mysql_errno = mysqli_errno( $this->dbh );
                                } else {
                                        // $dbh is defined, but isn't a real connection.
                                        // Something has gone horribly wrong, let's try a reconnect.
                                        $mysql_errno = 2006;
                                }
                        } else {
                                if ( is_resource( $this->dbh ) ) {
                                        $mysql_errno = mysql_errno( $this->dbh );
                                } else {
                                        $mysql_errno = 2006;
                                }
                        }
                }

                if ( empty( $this->dbh ) || 2006 == $mysql_errno ) {
                        if ( $this->check_connection() ) {
                                $this->_do_query( $query );
                        } else {
                                $this->insert_id = 0;
                                return false;
                        }
                }

                // If there is an error then take note of it.
                if ( $this->use_mysqli ) {
                        if ( $this->dbh instanceof mysqli ) {
                                $this->last_error = mysqli_error( $this->dbh );
                        } else {
                                $this->last_error = __( 'Unable to retrieve the error message from MySQL' );
                        }
                } else {
                        if ( is_resource( $this->dbh ) ) {
                                $this->last_error = mysql_error( $this->dbh );
                        } else {
                                $this->last_error = __( 'Unable to retrieve the error message from MySQL' );
                        }
                }

                if ( $this->last_error ) {
                        // Clear insert_id on a subsequent failed insert.
                        if ( $this->insert_id && preg_match( '/^\s*(insert|replace)\s/i', $query ) ) {
                                $this->insert_id = 0;
                        }

                        $this->print_error();
                        return false;
                }

                if ( preg_match( '/^\s*(create|alter|truncate|drop)\s/i', $query ) ) {
                        $return_val = $this->result;
                } elseif ( preg_match( '/^\s*(insert|delete|update|replace)\s/i', $query ) ) {
                        if ( $this->use_mysqli ) {
                                $this->rows_affected = mysqli_affected_rows( $this->dbh );
                        } else {
                                $this->rows_affected = mysql_affected_rows( $this->dbh );
                        }
                        // Take note of the insert_id
                        if ( preg_match( '/^\s*(insert|replace)\s/i', $query ) ) {
                                if ( $this->use_mysqli ) {
                                        $this->insert_id = mysqli_insert_id( $this->dbh );
                                } else {
                                        $this->insert_id = mysql_insert_id( $this->dbh );
                                }
                        }
                        // Return number of rows affected
                        $return_val = $this->rows_affected;
                } else {
                        $num_rows = 0;
                        if ( $this->use_mysqli && $this->result instanceof mysqli_result ) {
                                while ( $row = mysqli_fetch_object( $this->result ) ) {
                                        $this->last_result[ $num_rows ] = $row;
                                        $num_rows++;
                                }
                        } elseif ( is_resource( $this->result ) ) {
                                while ( $row = mysql_fetch_object( $this->result ) ) {
                                        $this->last_result[ $num_rows ] = $row;
                                        $num_rows++;
                                }
                        }

                        // Log number of rows the query returned
                        // and return number of rows selected
                        $this->num_rows = $num_rows;
                        $return_val     = $num_rows;
                }

                return $return_val;
        }

        /**
         * Internal function to perform the mysql_query() call.
         *
         * @since 3.9.0
         *
         * @see wpdb::query()
         *
         * @param string $query The query to run.
         */
        private function _do_query( $query ) {
                if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES ) {
                        $this->timer_start();
                }

                if ( ! empty( $this->dbh ) && $this->use_mysqli ) {
                        $this->result = mysqli_query( $this->dbh, $query );
                } elseif ( ! empty( $this->dbh ) ) {
                        $this->result = mysql_query( $query, $this->dbh );
                }
                $this->num_queries++;

                if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES ) {
                        $this->log_query(
                                $query,
                                $this->timer_stop(),
                                $this->get_caller(),
                                $this->time_start,
                                array()
                        );
                }
        }

        /**
         * Logs query data.
         *
         * @since 5.3.0
         *
         * @param string $query           The query's SQL.
         * @param float  $query_time      Total time spent on the query, in seconds.
         * @param string $query_callstack Comma separated list of the calling functions.
         * @param float  $query_start     Unix timestamp of the time at the start of the query.
         * @param array  $query_data      Custom query data.
         * }
         */
        public function log_query( $query, $query_time, $query_callstack, $query_start, $query_data ) {
                /**
                 * Filters the custom query data being logged.
                 *
                 * Caution should be used when modifying any of this data, it is recommended that any additional
                 * information you need to store about a query be added as a new associative entry to the fourth
                 * element $query_data.
                 *
                 * @since 5.3.0
                 *
                 * @param array  $query_data      Custom query data.
                 * @param string $query           The query's SQL.
                 * @param float  $query_time      Total time spent on the query, in seconds.
                 * @param string $query_callstack Comma separated list of the calling functions.
                 * @param float  $query_start     Unix timestamp of the time at the start of the query.
                 */
                $query_data = apply_filters( 'log_query_custom_data', $query_data, $query, $query_time, $query_callstack, $query_start );

                $this->queries[] = array(
                        $query,
                        $query_time,
                        $query_callstack,
                        $query_start,
                        $query_data,
                );
        }

        /**
         * Generates and returns a placeholder escape string for use in queries returned by ::prepare().
         *
         * @since 4.8.3
         *
         * @return string String to escape placeholders.
         */
        public function placeholder_escape() {
                static $placeholder;

                if ( ! $placeholder ) {
                        // If ext/hash is not present, compat.php's hash_hmac() does not support sha256.
                        $algo = function_exists( 'hash' ) ? 'sha256' : 'sha1';
                        // Old WP installs may not have AUTH_SALT defined.
                        $salt = defined( 'AUTH_SALT' ) && AUTH_SALT ? AUTH_SALT : (string) rand();

                        $placeholder = '{' . hash_hmac( $algo, uniqid( $salt, true ), $salt ) . '}';
                }

                /*
                 * Add the filter to remove the placeholder escaper. Uses priority 0, so that anything
                 * else attached to this filter will receive the query with the placeholder string removed.
                 */
                if ( false === has_filter( 'query', array( $this, 'remove_placeholder_escape' ) ) ) {
                        add_filter( 'query', array( $this, 'remove_placeholder_escape' ), 0 );
                }

                return $placeholder;
        }

        /**
         * Adds a placeholder escape string, to escape anything that resembles a printf() placeholder.
         *
         * @since 4.8.3
         *
         * @param string $query The query to escape.
         * @return string The query with the placeholder escape string inserted where necessary.
         */
        public function add_placeholder_escape( $query ) {
                /*
                 * To prevent returning anything that even vaguely resembles a placeholder,
                 * we clobber every % we can find.
                 */
                return str_replace( '%', $this->placeholder_escape(), $query );
        }

        /**
         * Removes the placeholder escape strings from a query.
         *
         * @since 4.8.3
         *
         * @param string $query The query from which the placeholder will be removed.
         * @return string The query with the placeholder removed.
         */
        public function remove_placeholder_escape( $query ) {
                return str_replace( $this->placeholder_escape(), '%', $query );
        }

        /**
         * Insert a row into a table.
         *
         *     wpdb::insert( 'table', array( 'column' => 'foo', 'field' => 'bar' ) )
         *     wpdb::insert( 'table', array( 'column' => 'foo', 'field' => 1337 ), array( '%s', '%d' ) )
         *
         * @since 2.5.0
         * @see wpdb::prepare()
         * @see wpdb::$field_types
         * @see wp_set_wpdb_vars()
         *
         * @param string       $table  Table name
         * @param array        $data   Data to insert (in column => value pairs).
         *                             Both $data columns and $data values should be "raw" (neither should be SQL escaped).
         *                             Sending a null value will cause the column to be set to NULL - the corresponding format is ignored in this case.
         * @param array|string $format Optional. An array of formats to be mapped to each of the value in $data.
         *                             If string, that format will be used for all of the values in $data.
         *                             A format is one of '%d', '%f', '%s' (integer, float, string).
         *                             If omitted, all values in $data will be treated as strings unless otherwise specified in wpdb::$field_types.
         * @return int|false The number of rows inserted, or false on error.
         */
        public function insert( $table, $data, $format = null ) {
                return $this->_insert_replace_helper( $table, $data, $format, 'INSERT' );
        }

        /**
         * Replace a row into a table.
         *
         *     wpdb::replace( 'table', array( 'column' => 'foo', 'field' => 'bar' ) )
         *     wpdb::replace( 'table', array( 'column' => 'foo', 'field' => 1337 ), array( '%s', '%d' ) )
         *
         * @since 3.0.0
         * @see wpdb::prepare()
         * @see wpdb::$field_types
         * @see wp_set_wpdb_vars()
         *
         * @param string       $table  Table name
         * @param array        $data   Data to insert (in column => value pairs).
         *                             Both $data columns and $data values should be "raw" (neither should be SQL escaped).
         *                             Sending a null value will cause the column to be set to NULL - the corresponding format is ignored in this case.
         * @param array|string $format Optional. An array of formats to be mapped to each of the value in $data.
         *                             If string, that format will be used for all of the values in $data.
         *                             A format is one of '%d', '%f', '%s' (integer, float, string).
         *                             If omitted, all values in $data will be treated as strings unless otherwise specified in wpdb::$field_types.
         * @return int|false The number of rows affected, or false on error.
         */
        public function replace( $table, $data, $format = null ) {
                return $this->_insert_replace_helper( $table, $data, $format, 'REPLACE' );
        }

        /**
         * Helper function for insert and replace.
         *
         * Runs an insert or replace query based on $type argument.
         *
         * @since 3.0.0
         * @see wpdb::prepare()
         * @see wpdb::$field_types
         * @see wp_set_wpdb_vars()
         *
         * @param string       $table  Table name
         * @param array        $data   Data to insert (in column => value pairs).
         *                             Both $data columns and $data values should be "raw" (neither should be SQL escaped).
         *                             Sending a null value will cause the column to be set to NULL - the corresponding format is ignored in this case.
         * @param array|string $format Optional. An array of formats to be mapped to each of the value in $data.
         *                             If string, that format will be used for all of the values in $data.
         *                             A format is one of '%d', '%f', '%s' (integer, float, string).
         *                             If omitted, all values in $data will be treated as strings unless otherwise specified in wpdb::$field_types.
         * @param string $type         Optional. What type of operation is this? INSERT or REPLACE. Defaults to INSERT.
         * @return int|false The number of rows affected, or false on error.
         */
        function _insert_replace_helper( $table, $data, $format = null, $type = 'INSERT' ) {
                $this->insert_id = 0;

                if ( ! in_array( strtoupper( $type ), array( 'REPLACE', 'INSERT' ) ) ) {
                        return false;
                }

                $data = $this->process_fields( $table, $data, $format );
                if ( false === $data ) {
                        return false;
                }

                $formats = array();
                $values  = array();
                foreach ( $data as $value ) {
                        if ( is_null( $value['value'] ) ) {
                                $formats[] = 'NULL';
                                continue;
                        }

                        $formats[] = $value['format'];
                        $values[]  = $value['value'];
                }

                $fields  = '`' . implode( '`, `', array_keys( $data ) ) . '`';
                $formats = implode( ', ', $formats );

                $sql = "$type INTO `$table` ($fields) VALUES ($formats)";

                $this->check_current_query = false;
                return $this->query( $this->prepare( $sql, $values ) );
        }

        /**
         * Update a row in the table
         *
         *     wpdb::update( 'table', array( 'column' => 'foo', 'field' => 'bar' ), array( 'ID' => 1 ) )
         *     wpdb::update( 'table', array( 'column' => 'foo', 'field' => 1337 ), array( 'ID' => 1 ), array( '%s', '%d' ), array( '%d' ) )
         *
         * @since 2.5.0
         * @see wpdb::prepare()
         * @see wpdb::$field_types
         * @see wp_set_wpdb_vars()
         *
         * @param string       $table        Table name
         * @param array        $data         Data to update (in column => value pairs).
         *                                   Both $data columns and $data values should be "raw" (neither should be SQL escaped).
         *                                   Sending a null value will cause the column to be set to NULL - the corresponding
         *                                   format is ignored in this case.
         * @param array        $where        A named array of WHERE clauses (in column => value pairs).
         *                                   Multiple clauses will be joined with ANDs.
         *                                   Both $where columns and $where values should be "raw".
         *                                   Sending a null value will create an IS NULL comparison - the corresponding format will be ignored in this case.
         * @param array|string $format       Optional. An array of formats to be mapped to each of the values in $data.
         *                                   If string, that format will be used for all of the values in $data.
         *                                   A format is one of '%d', '%f', '%s' (integer, float, string).
         *                                   If omitted, all values in $data will be treated as strings unless otherwise specified in wpdb::$field_types.
         * @param array|string $where_format Optional. An array of formats to be mapped to each of the values in $where.
         *                                   If string, that format will be used for all of the items in $where.
         *                                   A format is one of '%d', '%f', '%s' (integer, float, string).
         *                                   If omitted, all values in $where will be treated as strings.
         * @return int|false The number of rows updated, or false on error.
         */
        public function update( $table, $data, $where, $format = null, $where_format = null ) {
                if ( ! is_array( $data ) || ! is_array( $where ) ) {
                        return false;
                }

                $data = $this->process_fields( $table, $data, $format );
                if ( false === $data ) {
                        return false;
                }
                $where = $this->process_fields( $table, $where, $where_format );
                if ( false === $where ) {
                        return false;
                }

                $fields     = array();
                $conditions = array();
                $values     = array();
                foreach ( $data as $field => $value ) {
                        if ( is_null( $value['value'] ) ) {
                                $fields[] = "`$field` = NULL";
                                continue;
                        }

                        $fields[] = "`$field` = " . $value['format'];
                        $values[] = $value['value'];
                }
                foreach ( $where as $field => $value ) {
                        if ( is_null( $value['value'] ) ) {
                                $conditions[] = "`$field` IS NULL";
                                continue;
                        }

                        $conditions[] = "`$field` = " . $value['format'];
                        $values[]     = $value['value'];
                }

                $fields     = implode( ', ', $fields );
                $conditions = implode( ' AND ', $conditions );

                $sql = "UPDATE `$table` SET $fields WHERE $conditions";

                $this->check_current_query = false;
                return $this->query( $this->prepare( $sql, $values ) );
        }

        /**
         * Delete a row in the table
         *
         *     wpdb::delete( 'table', array( 'ID' => 1 ) )
         *     wpdb::delete( 'table', array( 'ID' => 1 ), array( '%d' ) )
         *
         * @since 3.4.0
         * @see wpdb::prepare()
         * @see wpdb::$field_types
         * @see wp_set_wpdb_vars()
         *
         * @param string       $table        Table name
         * @param array        $where        A named array of WHERE clauses (in column => value pairs).
         *                                   Multiple clauses will be joined with ANDs.
         *                                   Both $where columns and $where values should be "raw".
         *                                   Sending a null value will create an IS NULL comparison - the corresponding format will be ignored in this case.
         * @param array|string $where_format Optional. An array of formats to be mapped to each of the values in $where.
         *                                   If string, that format will be used for all of the items in $where.
         *                                   A format is one of '%d', '%f', '%s' (integer, float, string).
         *                                   If omitted, all values in $where will be treated as strings unless otherwise specified in wpdb::$field_types.
         * @return int|false The number of rows updated, or false on error.
         */
        public function delete( $table, $where, $where_format = null ) {
                if ( ! is_array( $where ) ) {
                        return false;
                }

                $where = $this->process_fields( $table, $where, $where_format );
                if ( false === $where ) {
                        return false;
                }

                $conditions = array();
                $values     = array();
                foreach ( $where as $field => $value ) {
                        if ( is_null( $value['value'] ) ) {
                                $conditions[] = "`$field` IS NULL";
                                continue;
                        }

                        $conditions[] = "`$field` = " . $value['format'];
                        $values[]     = $value['value'];
                }

                $conditions = implode( ' AND ', $conditions );

                $sql = "DELETE FROM `$table` WHERE $conditions";

                $this->check_current_query = false;
                return $this->query( $this->prepare( $sql, $values ) );
        }

        /**
         * Processes arrays of field/value pairs and field formats.
         *
         * This is a helper method for wpdb's CRUD methods, which take field/value
         * pairs for inserts, updates, and where clauses. This method first pairs
         * each value with a format. Then it determines the charset of that field,
         * using that to determine if any invalid text would be stripped. If text is
         * stripped, then field processing is rejected and the query fails.
         *
         * @since 4.2.0
         *
         * @param string $table  Table name.
         * @param array  $data   Field/value pair.
         * @param mixed  $format Format for each field.
         * @return array|false Returns an array of fields that contain paired values
         *                    and formats. Returns false for invalid values.
         */
        protected function process_fields( $table, $data, $format ) {
                $data = $this->process_field_formats( $data, $format );
                if ( false === $data ) {
                        return false;
                }

                $data = $this->process_field_charsets( $data, $table );
                if ( false === $data ) {
                        return false;
                }

                $data = $this->process_field_lengths( $data, $table );
                if ( false === $data ) {
                        return false;
                }

                $converted_data = $this->strip_invalid_text( $data );

                if ( $data !== $converted_data ) {
                        return false;
                }

                return $data;
        }

        /**
         * Prepares arrays of value/format pairs as passed to wpdb CRUD methods.
         *
         * @since 4.2.0
         *
         * @param array $data   Array of fields to values.
         * @param mixed $format Formats to be mapped to the values in $data.
         * @return array Array, keyed by field names with values being an array
         *               of 'value' and 'format' keys.
         */
        protected function process_field_formats( $data, $format ) {
                $formats          = (array) $format;
                $original_formats = $formats;

                foreach ( $data as $field => $value ) {
                        $value = array(
                                'value'  => $value,
                                'format' => '%s',
                        );

                        if ( ! empty( $format ) ) {
                                $value['format'] = array_shift( $formats );
                                if ( ! $value['format'] ) {
                                        $value['format'] = reset( $original_formats );
                                }
                        } elseif ( isset( $this->field_types[ $field ] ) ) {
                                $value['format'] = $this->field_types[ $field ];
                        }

                        $data[ $field ] = $value;
                }

                return $data;
        }

        /**
         * Adds field charsets to field/value/format arrays generated by
         * the wpdb::process_field_formats() method.
         *
         * @since 4.2.0
         *
         * @param array  $data  As it comes from the wpdb::process_field_formats() method.
         * @param string $table Table name.
         * @return array|false The same array as $data with additional 'charset' keys.
         */
        protected function process_field_charsets( $data, $table ) {
                foreach ( $data as $field => $value ) {
                        if ( '%d' === $value['format'] || '%f' === $value['format'] ) {
                                /*
                                 * We can skip this field if we know it isn't a string.
                                 * This checks %d/%f versus ! %s because its sprintf() could take more.
                                 */
                                $value['charset'] = false;
                        } else {
                                $value['charset'] = $this->get_col_charset( $table, $field );
                                if ( is_wp_error( $value['charset'] ) ) {
                                        return false;
                                }
                        }

                        $data[ $field ] = $value;
                }

                return $data;
        }

        /**
         * For string fields, record the maximum string length that field can safely save.
         *
         * @since 4.2.1
         *
         * @param array  $data  As it comes from the wpdb::process_field_charsets() method.
         * @param string $table Table name.
         * @return array|false The same array as $data with additional 'length' keys, or false if
         *                     any of the values were too long for their corresponding field.
         */
        protected function process_field_lengths( $data, $table ) {
                foreach ( $data as $field => $value ) {
                        if ( '%d' === $value['format'] || '%f' === $value['format'] ) {
                                /*
                                 * We can skip this field if we know it isn't a string.
                                 * This checks %d/%f versus ! %s because its sprintf() could take more.
                                 */
                                $value['length'] = false;
                        } else {
                                $value['length'] = $this->get_col_length( $table, $field );
                                if ( is_wp_error( $value['length'] ) ) {
                                        return false;
                                }
                        }

                        $data[ $field ] = $value;
                }

                return $data;
        }

        /**
         * Retrieve one variable from the database.
         *
         * Executes a SQL query and returns the value from the SQL result.
         * If the SQL result contains more than one column and/or more than one row, this function returns the value in the column and row specified.
         * If $query is null, this function returns the value in the specified column and row from the previous SQL result.
         *
         * @since 0.71
         *
         * @param string|null $query Optional. SQL query. Defaults to null, use the result from the previous query.
         * @param int         $x     Optional. Column of value to return. Indexed from 0.
         * @param int         $y     Optional. Row of value to return. Indexed from 0.
         * @return string|null Database query result (as string), or null on failure
         */
        public function get_var( $query = null, $x = 0, $y = 0 ) {
                $this->func_call = "\$db->get_var(\"$query\", $x, $y)";

                if ( $this->check_current_query && $this->check_safe_collation( $query ) ) {
                        $this->check_current_query = false;
                }

                if ( $query ) {
                        $this->query( $query );
                }

                // Extract var out of cached results based x,y vals
                if ( ! empty( $this->last_result[ $y ] ) ) {
                        $values = array_values( get_object_vars( $this->last_result[ $y ] ) );
                }

                // If there is a value return it else return null
                return ( isset( $values[ $x ] ) && $values[ $x ] !== '' ) ? $values[ $x ] : null;
        }

        /**
         * Retrieve one row from the database.
         *
         * Executes a SQL query and returns the row from the SQL result.
         *
         * @since 0.71
         *
         * @param string|null $query  SQL query.
         * @param string      $output Optional. The required return type. One of OBJECT, ARRAY_A, or ARRAY_N, which correspond to
         *                            an stdClass object, an associative array, or a numeric array, respectively. Default OBJECT.
         * @param int         $y      Optional. Row to return. Indexed from 0.
         * @return array|object|null|void Database query result in format specified by $output or null on failure
         */
        public function get_row( $query = null, $output = OBJECT, $y = 0 ) {
                $this->func_call = "\$db->get_row(\"$query\",$output,$y)";

                if ( $this->check_current_query && $this->check_safe_collation( $query ) ) {
                        $this->check_current_query = false;
                }

                if ( $query ) {
                        $this->query( $query );
                } else {
                        return null;
                }

                if ( ! isset( $this->last_result[ $y ] ) ) {
                        return null;
                }

                if ( $output == OBJECT ) {
                        return $this->last_result[ $y ] ? $this->last_result[ $y ] : null;
                } elseif ( $output == ARRAY_A ) {
                        return $this->last_result[ $y ] ? get_object_vars( $this->last_result[ $y ] ) : null;
                } elseif ( $output == ARRAY_N ) {
                        return $this->last_result[ $y ] ? array_values( get_object_vars( $this->last_result[ $y ] ) ) : null;
                } elseif ( strtoupper( $output ) === OBJECT ) {
                        // Back compat for OBJECT being previously case insensitive.
                        return $this->last_result[ $y ] ? $this->last_result[ $y ] : null;
                } else {
                        $this->print_error( ' $db->get_row(string query, output type, int offset) -- Output type must be one of: OBJECT, ARRAY_A, ARRAY_N' );
                }
        }

        /**
         * Retrieve one column from the database.
         *
         * Executes a SQL query and returns the column from the SQL result.
         * If the SQL result contains more than one column, this function returns the column specified.
         * If $query is null, this function returns the specified column from the previous SQL result.
         *
         * @since 0.71
         *
         * @param string|null $query Optional. SQL query. Defaults to previous query.
         * @param int         $x     Optional. Column to return. Indexed from 0.
         * @return array Database query result. Array indexed from 0 by SQL result row number.
         */
        public function get_col( $query = null, $x = 0 ) {
                if ( $this->check_current_query && $this->check_safe_collation( $query ) ) {
                        $this->check_current_query = false;
                }

                if ( $query ) {
                        $this->query( $query );
                }

                $new_array = array();
                // Extract the column values
                if ( $this->last_result ) {
                        for ( $i = 0, $j = count( $this->last_result ); $i < $j; $i++ ) {
                                $new_array[ $i ] = $this->get_var( null, $x, $i );
                        }
                }
                return $new_array;
        }

        /**
         * Retrieve an entire SQL result set from the database (i.e., many rows)
         *
         * Executes a SQL query and returns the entire SQL result.
         *
         * @since 0.71
         *
         * @param string $query  SQL query.
         * @param string $output Optional. Any of ARRAY_A | ARRAY_N | OBJECT | OBJECT_K constants.
         *                       With one of the first three, return an array of rows indexed from 0 by SQL result row number.
         *                       Each row is an associative array (column => value, ...), a numerically indexed array (0 => value, ...), or an object. ( ->column = value ), respectively.
         *                       With OBJECT_K, return an associative array of row objects keyed by the value of each row's first column's value.
         *                       Duplicate keys are discarded.
         * @return array|object|null Database query results
         */
        public function get_results( $query = null, $output = OBJECT ) {
                $this->func_call = "\$db->get_results(\"$query\", $output)";

                if ( $this->check_current_query && $this->check_safe_collation( $query ) ) {
                        $this->check_current_query = false;
                }

                if ( $query ) {
                        $this->query( $query );
                } else {
                        return null;
                }

                $new_array = array();
                if ( $output == OBJECT ) {
                        // Return an integer-keyed array of row objects
                        return $this->last_result;
                } elseif ( $output == OBJECT_K ) {
                        // Return an array of row objects with keys from column 1
                        // (Duplicates are discarded)
                        if ( $this->last_result ) {
                                foreach ( $this->last_result as $row ) {
                                        $var_by_ref = get_object_vars( $row );
                                        $key        = array_shift( $var_by_ref );
                                        if ( ! isset( $new_array[ $key ] ) ) {
                                                $new_array[ $key ] = $row;
                                        }
                                }
                        }
                        return $new_array;
                } elseif ( $output == ARRAY_A || $output == ARRAY_N ) {
                        // Return an integer-keyed array of...
                        if ( $this->last_result ) {
                                foreach ( (array) $this->last_result as $row ) {
                                        if ( $output == ARRAY_N ) {
                                                // ...integer-keyed row arrays
                                                $new_array[] = array_values( get_object_vars( $row ) );
                                        } else {
                                                // ...column name-keyed row arrays
                                                $new_array[] = get_object_vars( $row );
                                        }
                                }
                        }
                        return $new_array;
                } elseif ( strtoupper( $output ) === OBJECT ) {
                        // Back compat for OBJECT being previously case insensitive.
                        return $this->last_result;
                }
                return null;
        }

        /**
         * Retrieves the character set for the given table.
         *
         * @since 4.2.0
         *
         * @param string $table Table name.
         * @return string|WP_Error Table character set, WP_Error object if it couldn't be found.
         */
        protected function get_table_charset( $table ) {
                $tablekey = strtolower( $table );

                /**
                 * Filters the table charset value before the DB is checked.
                 *
                 * Passing a non-null value to the filter will effectively short-circuit
                 * checking the DB for the charset, returning that value instead.
                 *
                 * @since 4.2.0
                 *
                 * @param string|null $charset The character set to use. Default null.
                 * @param string      $table   The name of the table being checked.
                 */
                $charset = apply_filters( 'pre_get_table_charset', null, $table );
                if ( null !== $charset ) {
                        return $charset;
                }

                if ( isset( $this->table_charset[ $tablekey ] ) ) {
                        return $this->table_charset[ $tablekey ];
                }

                $charsets = array();
                $columns  = array();

                $table_parts = explode( '.', $table );
                $table       = '`' . implode( '`.`', $table_parts ) . '`';
                $results     = $this->get_results( "SHOW FULL COLUMNS FROM $table" );
                if ( ! $results ) {
                        return new WP_Error( 'wpdb_get_table_charset_failure' );
                }

                foreach ( $results as $column ) {
                        $columns[ strtolower( $column->Field ) ] = $column;
                }

                $this->col_meta[ $tablekey ] = $columns;

                foreach ( $columns as $column ) {
                        if ( ! empty( $column->Collation ) ) {
                                list( $charset ) = explode( '_', $column->Collation );

                                // If the current connection can't support utf8mb4 characters, let's only send 3-byte utf8 characters.
                                if ( 'utf8mb4' === $charset && ! $this->has_cap( 'utf8mb4' ) ) {
                                        $charset = 'utf8';
                                }

                                $charsets[ strtolower( $charset ) ] = true;
                        }

                        list( $type ) = explode( '(', $column->Type );

                        // A binary/blob means the whole query gets treated like this.
                        if ( in_array( strtoupper( $type ), array( 'BINARY', 'VARBINARY', 'TINYBLOB', 'MEDIUMBLOB', 'BLOB', 'LONGBLOB' ) ) ) {
                                $this->table_charset[ $tablekey ] = 'binary';
                                return 'binary';
                        }
                }

                // utf8mb3 is an alias for utf8.
                if ( isset( $charsets['utf8mb3'] ) ) {
                        $charsets['utf8'] = true;
                        unset( $charsets['utf8mb3'] );
                }

                // Check if we have more than one charset in play.
                $count = count( $charsets );
                if ( 1 === $count ) {
                        $charset = key( $charsets );
                } elseif ( 0 === $count ) {
                        // No charsets, assume this table can store whatever.
                        $charset = false;
                } else {
                        // More than one charset. Remove latin1 if present and recalculate.
                        unset( $charsets['latin1'] );
                        $count = count( $charsets );
                        if ( 1 === $count ) {
                                // Only one charset (besides latin1).
                                $charset = key( $charsets );
                        } elseif ( 2 === $count && isset( $charsets['utf8'], $charsets['utf8mb4'] ) ) {
                                // Two charsets, but they're utf8 and utf8mb4, use utf8.
                                $charset = 'utf8';
                        } else {
                                // Two mixed character sets. ascii.
                                $charset = 'ascii';
                        }
                }

                $this->table_charset[ $tablekey ] = $charset;
                return $charset;
        }

        /**
         * Retrieves the character set for the given column.
         *
         * @since 4.2.0
         *
         * @param string $table  Table name.
         * @param string $column Column name.
         * @return string|false|WP_Error Column character set as a string. False if the column has no
         *                               character set. WP_Error object if there was an error.
         */
        public function get_col_charset( $table, $column ) {
                $tablekey  = strtolower( $table );
                $columnkey = strtolower( $column );

                /**
                 * Filters the column charset value before the DB is checked.
                 *
                 * Passing a non-null value to the filter will short-circuit
                 * checking the DB for the charset, returning that value instead.
                 *
                 * @since 4.2.0
                 *
                 * @param string|null $charset The character set to use. Default null.
                 * @param string      $table   The name of the table being checked.
                 * @param string      $column  The name of the column being checked.
                 */
                $charset = apply_filters( 'pre_get_col_charset', null, $table, $column );
                if ( null !== $charset ) {
                        return $charset;
                }

                // Skip this entirely if this isn't a MySQL database.
                if ( empty( $this->is_mysql ) ) {
                        return false;
                }

                if ( empty( $this->table_charset[ $tablekey ] ) ) {
                        // This primes column information for us.
                        $table_charset = $this->get_table_charset( $table );
                        if ( is_wp_error( $table_charset ) ) {
                                return $table_charset;
                        }
                }

                // If still no column information, return the table charset.
                if ( empty( $this->col_meta[ $tablekey ] ) ) {
                        return $this->table_charset[ $tablekey ];
                }

                // If this column doesn't exist, return the table charset.
                if ( empty( $this->col_meta[ $tablekey ][ $columnkey ] ) ) {
                        return $this->table_charset[ $tablekey ];
                }

                // Return false when it's not a string column.
                if ( empty( $this->col_meta[ $tablekey ][ $columnkey ]->Collation ) ) {
                        return false;
                }

                list( $charset ) = explode( '_', $this->col_meta[ $tablekey ][ $columnkey ]->Collation );
                return $charset;
        }

        /**
         * Retrieve the maximum string length allowed in a given column.
         * The length may either be specified as a byte length or a character length.
         *
         * @since 4.2.1
         *
         * @param string $table  Table name.
         * @param string $column Column name.
         * @return array|false|WP_Error array( 'length' => (int), 'type' => 'byte' | 'char' )
         *                              false if the column has no length (for example, numeric column)
         *                              WP_Error object if there was an error.
         */
        public function get_col_length( $table, $column ) {
                $tablekey  = strtolower( $table );
                $columnkey = strtolower( $column );

                // Skip this entirely if this isn't a MySQL database.
                if ( empty( $this->is_mysql ) ) {
                        return false;
                }

                if ( empty( $this->col_meta[ $tablekey ] ) ) {
                        // This primes column information for us.
                        $table_charset = $this->get_table_charset( $table );
                        if ( is_wp_error( $table_charset ) ) {
                                return $table_charset;
                        }
                }

                if ( empty( $this->col_meta[ $tablekey ][ $columnkey ] ) ) {
                        return false;
                }

                $typeinfo = explode( '(', $this->col_meta[ $tablekey ][ $columnkey ]->Type );

                $type = strtolower( $typeinfo[0] );
                if ( ! empty( $typeinfo[1] ) ) {
                        $length = trim( $typeinfo[1], ')' );
                } else {
                        $length = false;
                }

                switch ( $type ) {
                        case 'char':
                        case 'varchar':
                                return array(
                                        'type'   => 'char',
                                        'length' => (int) $length,
                                );

                        case 'binary':
                        case 'varbinary':
                                return array(
                                        'type'   => 'byte',
                                        'length' => (int) $length,
                                );

                        case 'tinyblob':
                        case 'tinytext':
                                return array(
                                        'type'   => 'byte',
                                        'length' => 255,        // 2^8 - 1
                                );

                        case 'blob':
                        case 'text':
                                return array(
                                        'type'   => 'byte',
                                        'length' => 65535,      // 2^16 - 1
                                );

                        case 'mediumblob':
                        case 'mediumtext':
                                return array(
                                        'type'   => 'byte',
                                        'length' => 16777215,   // 2^24 - 1
                                );

                        case 'longblob':
                        case 'longtext':
                                return array(
                                        'type'   => 'byte',
                                        'length' => 4294967295, // 2^32 - 1
                                );

                        default:
                                return false;
                }
        }

        /**
         * Check if a string is ASCII.
         *
         * The negative regex is faster for non-ASCII strings, as it allows
         * the search to finish as soon as it encounters a non-ASCII character.
         *
         * @since 4.2.0
         *
         * @param string $string String to check.
         * @return bool True if ASCII, false if not.
         */
        protected function check_ascii( $string ) {
                if ( function_exists( 'mb_check_encoding' ) ) {
                        if ( mb_check_encoding( $string, 'ASCII' ) ) {
                                return true;
                        }
                } elseif ( ! preg_match( '/[^\x00-\x7F]/', $string ) ) {
                        return true;
                }

                return false;
        }

        /**
         * Check if the query is accessing a collation considered safe on the current version of MySQL.
         *
         * @since 4.2.0
         *
         * @param string $query The query to check.
         * @return bool True if the collation is safe, false if it isn't.
         */
        protected function check_safe_collation( $query ) {
                if ( $this->checking_collation ) {
                        return true;
                }

                // We don't need to check the collation for queries that don't read data.
                $query = ltrim( $query, "\r\n\t (" );
                if ( preg_match( '/^(?:SHOW|DESCRIBE|DESC|EXPLAIN|CREATE)\s/i', $query ) ) {
                        return true;
                }

                // All-ASCII queries don't need extra checking.
                if ( $this->check_ascii( $query ) ) {
                        return true;
                }

                $table = $this->get_table_from_query( $query );
                if ( ! $table ) {
                        return false;
                }

                $this->checking_collation = true;
                $collation                = $this->get_table_charset( $table );
                $this->checking_collation = false;

                // Tables with no collation, or latin1 only, don't need extra checking.
                if ( false === $collation || 'latin1' === $collation ) {
                        return true;
                }

                $table = strtolower( $table );
                if ( empty( $this->col_meta[ $table ] ) ) {
                        return false;
                }

                // If any of the columns don't have one of these collations, it needs more sanity checking.
                foreach ( $this->col_meta[ $table ] as $col ) {
                        if ( empty( $col->Collation ) ) {
                                continue;
                        }

                        if ( ! in_array( $col->Collation, array( 'utf8_general_ci', 'utf8_bin', 'utf8mb4_general_ci', 'utf8mb4_bin' ), true ) ) {
                                return false;
                        }
                }

                return true;
        }

        /**
         * Strips any invalid characters based on value/charset pairs.
         *
         * @since 4.2.0
         *
         * @param array $data Array of value arrays. Each value array has the keys
         *                    'value' and 'charset'. An optional 'ascii' key can be
         *                    set to false to avoid redundant ASCII checks.
         * @return array|WP_Error The $data parameter, with invalid characters removed from
         *                        each value. This works as a passthrough: any additional keys
         *                        such as 'field' are retained in each value array. If we cannot
         *                        remove invalid characters, a WP_Error object is returned.
         */
        protected function strip_invalid_text( $data ) {
                $db_check_string = false;

                foreach ( $data as &$value ) {
                        $charset = $value['charset'];

                        if ( is_array( $value['length'] ) ) {
                                $length                  = $value['length']['length'];
                                $truncate_by_byte_length = 'byte' === $value['length']['type'];
                        } else {
                                $length = false;
                                // Since we have no length, we'll never truncate.
                                // Initialize the variable to false. true would take us
                                // through an unnecessary (for this case) codepath below.
                                $truncate_by_byte_length = false;
                        }

                        // There's no charset to work with.
                        if ( false === $charset ) {
                                continue;
                        }

                        // Column isn't a string.
                        if ( ! is_string( $value['value'] ) ) {
                                continue;
                        }

                        $needs_validation = true;
                        if (
                                // latin1 can store any byte sequence
                                'latin1' === $charset
                        ||
                                // ASCII is always OK.
                                ( ! isset( $value['ascii'] ) && $this->check_ascii( $value['value'] ) )
                        ) {
                                $truncate_by_byte_length = true;
                                $needs_validation        = false;
                        }

                        if ( $truncate_by_byte_length ) {
                                mbstring_binary_safe_encoding();
                                if ( false !== $length && strlen( $value['value'] ) > $length ) {
                                        $value['value'] = substr( $value['value'], 0, $length );
                                }
                                reset_mbstring_encoding();

                                if ( ! $needs_validation ) {
                                        continue;
                                }
                        }

                        // utf8 can be handled by regex, which is a bunch faster than a DB lookup.
                        if ( ( 'utf8' === $charset || 'utf8mb3' === $charset || 'utf8mb4' === $charset ) && function_exists( 'mb_strlen' ) ) {
                                $regex = '/
                                        (
                                                (?: [\x00-\x7F]                  # single-byte sequences   0xxxxxxx
                                                |   [\xC2-\xDF][\x80-\xBF]       # double-byte sequences   110xxxxx 10xxxxxx
                                                |   \xE0[\xA0-\xBF][\x80-\xBF]   # triple-byte sequences   1110xxxx 10xxxxxx * 2
                                                |   [\xE1-\xEC][\x80-\xBF]{2}
                                                |   \xED[\x80-\x9F][\x80-\xBF]
                                                |   [\xEE-\xEF][\x80-\xBF]{2}';

                                if ( 'utf8mb4' === $charset ) {
                                        $regex .= '
                                                |    \xF0[\x90-\xBF][\x80-\xBF]{2} # four-byte sequences   11110xxx 10xxxxxx * 3
                                                |    [\xF1-\xF3][\x80-\xBF]{3}
                                                |    \xF4[\x80-\x8F][\x80-\xBF]{2}
                                        ';
                                }

                                $regex         .= '){1,40}                          # ...one or more times
                                        )
                                        | .                                  # anything else
                                        /x';
                                $value['value'] = preg_replace( $regex, '$1', $value['value'] );

                                if ( false !== $length && mb_strlen( $value['value'], 'UTF-8' ) > $length ) {
                                        $value['value'] = mb_substr( $value['value'], 0, $length, 'UTF-8' );
                                }
                                continue;
                        }

                        // We couldn't use any local conversions, send it to the DB.
                        $value['db']     = true;
                        $db_check_string = true;
                }
                unset( $value ); // Remove by reference.

                if ( $db_check_string ) {
                        $queries = array();
                        foreach ( $data as $col => $value ) {
                                if ( ! empty( $value['db'] ) ) {
                                        // We're going to need to truncate by characters or bytes, depending on the length value we have.
                                        if ( isset( $value['length']['type'] ) && 'byte' === $value['length']['type'] ) {
                                                // Using binary causes LEFT() to truncate by bytes.
                                                $charset = 'binary';
                                        } else {
                                                $charset = $value['charset'];
                                        }

                                        if ( $this->charset ) {
                                                $connection_charset = $this->charset;
                                        } else {
                                                if ( $this->use_mysqli ) {
                                                        $connection_charset = mysqli_character_set_name( $this->dbh );
                                                } else {
                                                        $connection_charset = mysql_client_encoding();
                                                }
                                        }

                                        if ( is_array( $value['length'] ) ) {
                                                $length          = sprintf( '%.0f', $value['length']['length'] );
                                                $queries[ $col ] = $this->prepare( "CONVERT( LEFT( CONVERT( %s USING $charset ), $length ) USING $connection_charset )", $value['value'] );
                                        } elseif ( 'binary' !== $charset ) {
                                                // If we don't have a length, there's no need to convert binary - it will always return the same result.
                                                $queries[ $col ] = $this->prepare( "CONVERT( CONVERT( %s USING $charset ) USING $connection_charset )", $value['value'] );
                                        }

                                        unset( $data[ $col ]['db'] );
                                }
                        }

                        $sql = array();
                        foreach ( $queries as $column => $query ) {
                                if ( ! $query ) {
                                        continue;
                                }

                                $sql[] = $query . " AS x_$column";
                        }

                        $this->check_current_query = false;
                        $row                       = $this->get_row( 'SELECT ' . implode( ', ', $sql ), ARRAY_A );
                        if ( ! $row ) {
                                return new WP_Error( 'wpdb_strip_invalid_text_failure' );
                        }

                        foreach ( array_keys( $data ) as $column ) {
                                if ( isset( $row[ "x_$column" ] ) ) {
                                        $data[ $column ]['value'] = $row[ "x_$column" ];
                                }
                        }
                }

                return $data;
        }

        /**
         * Strips any invalid characters from the query.
         *
         * @since 4.2.0
         *
         * @param string $query Query to convert.
         * @return string|WP_Error The converted query, or a WP_Error object if the conversion fails.
         */
        protected function strip_invalid_text_from_query( $query ) {
                // We don't need to check the collation for queries that don't read data.
                $trimmed_query = ltrim( $query, "\r\n\t (" );
                if ( preg_match( '/^(?:SHOW|DESCRIBE|DESC|EXPLAIN|CREATE)\s/i', $trimmed_query ) ) {
                        return $query;
                }

                $table = $this->get_table_from_query( $query );
                if ( $table ) {
                        $charset = $this->get_table_charset( $table );
                        if ( is_wp_error( $charset ) ) {
                                return $charset;
                        }

                        // We can't reliably strip text from tables containing binary/blob columns
                        if ( 'binary' === $charset ) {
                                return $query;
                        }
                } else {
                        $charset = $this->charset;
                }

                $data = array(
                        'value'   => $query,
                        'charset' => $charset,
                        'ascii'   => false,
                        'length'  => false,
                );

                $data = $this->strip_invalid_text( array( $data ) );
                if ( is_wp_error( $data ) ) {
                        return $data;
                }

                return $data[0]['value'];
        }

        /**
         * Strips any invalid characters from the string for a given table and column.
         *
         * @since 4.2.0
         *
         * @param string $table  Table name.
         * @param string $column Column name.
         * @param string $value  The text to check.
         * @return string|WP_Error The converted string, or a WP_Error object if the conversion fails.
         */
        public function strip_invalid_text_for_column( $table, $column, $value ) {
                if ( ! is_string( $value ) ) {
                        return $value;
                }

                $charset = $this->get_col_charset( $table, $column );
                if ( ! $charset ) {
                        // Not a string column.
                        return $value;
                } elseif ( is_wp_error( $charset ) ) {
                        // Bail on real errors.
                        return $charset;
                }

                $data = array(
                        $column => array(
                                'value'   => $value,
                                'charset' => $charset,
                                'length'  => $this->get_col_length( $table, $column ),
                        ),
                );

                $data = $this->strip_invalid_text( $data );
                if ( is_wp_error( $data ) ) {
                        return $data;
                }

                return $data[ $column ]['value'];
        }

        /**
         * Find the first table name referenced in a query.
         *
         * @since 4.2.0
         *
         * @param string $query The query to search.
         * @return string|false $table The table name found, or false if a table couldn't be found.
         */
        protected function get_table_from_query( $query ) {
                // Remove characters that can legally trail the table name.
                $query = rtrim( $query, ';/-#' );

                // Allow (select...) union [...] style queries. Use the first query's table name.
                $query = ltrim( $query, "\r\n\t (" );

                // Strip everything between parentheses except nested selects.
                $query = preg_replace( '/\((?!\s*select)[^(]*?\)/is', '()', $query );

                // Quickly match most common queries.
                if ( preg_match(
                        '/^\s*(?:'
                                . 'SELECT.*?\s+FROM'
                                . '|INSERT(?:\s+LOW_PRIORITY|\s+DELAYED|\s+HIGH_PRIORITY)?(?:\s+IGNORE)?(?:\s+INTO)?'
                                . '|REPLACE(?:\s+LOW_PRIORITY|\s+DELAYED)?(?:\s+INTO)?'
                                . '|UPDATE(?:\s+LOW_PRIORITY)?(?:\s+IGNORE)?'
                                . '|DELETE(?:\s+LOW_PRIORITY|\s+QUICK|\s+IGNORE)*(?:.+?FROM)?'
                        . ')\s+((?:[0-9a-zA-Z$_.`-]|[\xC2-\xDF][\x80-\xBF])+)/is',
                        $query,
                        $maybe
                ) ) {
                        return str_replace( '`', '', $maybe[1] );
                }

                // SHOW TABLE STATUS and SHOW TABLES WHERE Name = 'wp_posts'
                if ( preg_match( '/^\s*SHOW\s+(?:TABLE\s+STATUS|(?:FULL\s+)?TABLES).+WHERE\s+Name\s*=\s*("|\')((?:[0-9a-zA-Z$_.-]|[\xC2-\xDF][\x80-\xBF])+)\\1/is', $query, $maybe ) ) {
                        return $maybe[2];
                }

                // SHOW TABLE STATUS LIKE and SHOW TABLES LIKE 'wp\_123\_%'
                // This quoted LIKE operand seldom holds a full table name.
                // It is usually a pattern for matching a prefix so we just
                // strip the trailing % and unescape the _ to get 'wp_123_'
                // which drop-ins can use for routing these SQL statements.
                if ( preg_match( '/^\s*SHOW\s+(?:TABLE\s+STATUS|(?:FULL\s+)?TABLES)\s+(?:WHERE\s+Name\s+)?LIKE\s*("|\')((?:[\\\\0-9a-zA-Z$_.-]|[\xC2-\xDF][\x80-\xBF])+)%?\\1/is', $query, $maybe ) ) {
                        return str_replace( '\\_', '_', $maybe[2] );
                }

                // Big pattern for the rest of the table-related queries.
                if ( preg_match(
                        '/^\s*(?:'
                                . '(?:EXPLAIN\s+(?:EXTENDED\s+)?)?SELECT.*?\s+FROM'
                                . '|DESCRIBE|DESC|EXPLAIN|HANDLER'
                                . '|(?:LOCK|UNLOCK)\s+TABLE(?:S)?'
                                . '|(?:RENAME|OPTIMIZE|BACKUP|RESTORE|CHECK|CHECKSUM|ANALYZE|REPAIR).*\s+TABLE'
                                . '|TRUNCATE(?:\s+TABLE)?'
                                . '|CREATE(?:\s+TEMPORARY)?\s+TABLE(?:\s+IF\s+NOT\s+EXISTS)?'
                                . '|ALTER(?:\s+IGNORE)?\s+TABLE'
                                . '|DROP\s+TABLE(?:\s+IF\s+EXISTS)?'
                                . '|CREATE(?:\s+\w+)?\s+INDEX.*\s+ON'
                                . '|DROP\s+INDEX.*\s+ON'
                                . '|LOAD\s+DATA.*INFILE.*INTO\s+TABLE'
                                . '|(?:GRANT|REVOKE).*ON\s+TABLE'
                                . '|SHOW\s+(?:.*FROM|.*TABLE)'
                        . ')\s+\(*\s*((?:[0-9a-zA-Z$_.`-]|[\xC2-\xDF][\x80-\xBF])+)\s*\)*/is',
                        $query,
                        $maybe
                ) ) {
                        return str_replace( '`', '', $maybe[1] );
                }

                return false;
        }

        /**
         * Load the column metadata from the last query.
         *
         * @since 3.5.0
         */
        protected function load_col_info() {
                if ( $this->col_info ) {
                        return;
                }

                if ( $this->use_mysqli ) {
                        $num_fields = mysqli_num_fields( $this->result );
                        for ( $i = 0; $i < $num_fields; $i++ ) {
                                $this->col_info[ $i ] = mysqli_fetch_field( $this->result );
                        }
                } else {
                        $num_fields = mysql_num_fields( $this->result );
                        for ( $i = 0; $i < $num_fields; $i++ ) {
                                $this->col_info[ $i ] = mysql_fetch_field( $this->result, $i );
                        }
                }
        }

        /**
         * Retrieve column metadata from the last query.
         *
         * @since 0.71
         *
         * @param string $info_type  Optional. Type one of name, table, def, max_length, not_null, primary_key, multiple_key, unique_key, numeric, blob, type, unsigned, zerofill
         * @param int    $col_offset Optional. 0: col name. 1: which table the col's in. 2: col's max length. 3: if the col is numeric. 4: col's type
         * @return mixed Column Results
         */
        public function get_col_info( $info_type = 'name', $col_offset = -1 ) {
                $this->load_col_info();

                if ( $this->col_info ) {
                        if ( $col_offset == -1 ) {
                                $i         = 0;
                                $new_array = array();
                                foreach ( (array) $this->col_info as $col ) {
                                        $new_array[ $i ] = $col->{$info_type};
                                        $i++;
                                }
                                return $new_array;
                        } else {
                                return $this->col_info[ $col_offset ]->{$info_type};
                        }
                }
        }

        /**
         * Starts the timer, for debugging purposes.
         *
         * @since 1.5.0
         *
         * @return true
         */
        public function timer_start() {
                $this->time_start = microtime( true );
                return true;
        }

        /**
         * Stops the debugging timer.
         *
         * @since 1.5.0
         *
         * @return float Total time spent on the query, in seconds
         */
        public function timer_stop() {
                return ( microtime( true ) - $this->time_start );
        }

        /**
         * Wraps errors in a nice header and footer and dies.
         *
         * Will not die if wpdb::$show_errors is false.
         *
         * @since 1.5.0
         *
         * @param string $message    The Error message
         * @param string $error_code Optional. A Computer readable string to identify the error.
         * @return false|void
         */
        public function bail( $message, $error_code = '500' ) {
                if ( $this->show_errors ) {
                        $error = '';

                        if ( $this->use_mysqli ) {
                                if ( $this->dbh instanceof mysqli ) {
                                        $error = mysqli_error( $this->dbh );
                                } elseif ( mysqli_connect_errno() ) {
                                        $error = mysqli_connect_error();
                                }
                        } else {
                                if ( is_resource( $this->dbh ) ) {
                                        $error = mysql_error( $this->dbh );
                                } else {
                                        $error = mysql_error();
                                }
                        }

                        if ( $error ) {
                                $message = '<p><code>' . $error . "</code></p>\n" . $message;
                        }

                        wp_die( $message );
                } else {
                        if ( class_exists( 'WP_Error', false ) ) {
                                $this->error = new WP_Error( $error_code, $message );
                        } else {
                                $this->error = $message;
                        }

                        return false;
                }
        }


        /**
         * Closes the current database connection.
         *
         * @since 4.5.0
         *
         * @return bool True if the connection was successfully closed, false if it wasn't,
         *              or the connection doesn't exist.
         */
        public function close() {
                if ( ! $this->dbh ) {
                        return false;
                }

                if ( $this->use_mysqli ) {
                        $closed = mysqli_close( $this->dbh );
                } else {
                        $closed = mysql_close( $this->dbh );
                }

                if ( $closed ) {
                        $this->dbh           = null;
                        $this->ready         = false;
                        $this->has_connected = false;
                }

                return $closed;
        }

        /**
         * Whether MySQL database is at least the required minimum version.
         *
         * @since 2.5.0
         *
         * @global string $wp_version
         * @global string $required_mysql_version
         *
         * @return WP_Error|void
         */
        public function check_database_version() {
                global $wp_version, $required_mysql_version;
                // Make sure the server has the required MySQL version
                if ( version_compare( $this->db_version(), $required_mysql_version, '<' ) ) {
                        /* translators: 1: WordPress version number, 2: Minimum required MySQL version number. */
                        return new WP_Error( 'database_version', sprintf( __( '<strong>ERROR</strong>: WordPress %1$s requires MySQL %2$s or higher' ), $wp_version, $required_mysql_version ) );
                }
        }

        /**
         * Whether the database supports collation.
         *
         * Called when WordPress is generating the table scheme.
         *
         * Use `wpdb::has_cap( 'collation' )`.
         *
         * @since 2.5.0
         * @deprecated 3.5.0 Use wpdb::has_cap()
         *
         * @return bool True if collation is supported, false if version does not
         */
        public function supports_collation() {
                _deprecated_function( __FUNCTION__, '3.5.0', 'wpdb::has_cap( \'collation\' )' );
                return $this->has_cap( 'collation' );
        }

        /**
         * The database character collate.
         *
         * @since 3.5.0
         *
         * @return string The database character collate.
         */
        public function get_charset_collate() {
                $charset_collate = '';

                if ( ! empty( $this->charset ) ) {
                        $charset_collate = "DEFAULT CHARACTER SET $this->charset";
                }
                if ( ! empty( $this->collate ) ) {
                        $charset_collate .= " COLLATE $this->collate";
                }

                return $charset_collate;
        }

        /**
         * Determine if a database supports a particular feature.
         *
         * @since 2.7.0
         * @since 4.1.0 Added support for the 'utf8mb4' feature.
         * @since 4.6.0 Added support for the 'utf8mb4_520' feature.
         *
         * @see wpdb::db_version()
         *
         * @param string $db_cap The feature to check for. Accepts 'collation',
         *                       'group_concat', 'subqueries', 'set_charset',
         *                       'utf8mb4', or 'utf8mb4_520'.
         * @return int|false Whether the database feature is supported, false otherwise.
         */
        public function has_cap( $db_cap ) {
                $version = $this->db_version();

                switch ( strtolower( $db_cap ) ) {
                        case 'collation':    // @since 2.5.0
                        case 'group_concat': // @since 2.7.0
                        case 'subqueries':   // @since 2.7.0
                                return version_compare( $version, '4.1', '>=' );
                        case 'set_charset':
                                return version_compare( $version, '5.0.7', '>=' );
                        case 'utf8mb4':      // @since 4.1.0
                                if ( version_compare( $version, '5.5.3', '<' ) ) {
                                        return false;
                                }
                                if ( $this->use_mysqli ) {
                                        $client_version = mysqli_get_client_info();
                                } else {
                                        $client_version = mysql_get_client_info();
                                }

                                /*
                                 * libmysql has supported utf8mb4 since 5.5.3, same as the MySQL server.
                                 * mysqlnd has supported utf8mb4 since 5.0.9.
                                 */
                                if ( false !== strpos( $client_version, 'mysqlnd' ) ) {
                                        $client_version = preg_replace( '/^\D+([\d.]+).*/', '$1', $client_version );
                                        return version_compare( $client_version, '5.0.9', '>=' );
                                } else {
                                        return version_compare( $client_version, '5.5.3', '>=' );
                                }
                        case 'utf8mb4_520': // @since 4.6.0
                                return version_compare( $version, '5.6', '>=' );
                }

                return false;
        }

        /**
         * Retrieve the name of the function that called wpdb.
         *
         * Searches up the list of functions until it reaches
         * the one that would most logically had called this method.
         *
         * @since 2.5.0
         *
         * @return string Comma separated list of the calling functions.
         */
        public function get_caller() {
                return wp_debug_backtrace_summary( __CLASS__ );
        }

        /**
         * Retrieves the MySQL server version.
         *
         * @since 2.7.0
         *
         * @return null|string Null on failure, version number on success.
         */
        public function db_version() {
                if ( $this->use_mysqli ) {
                        $server_info = mysqli_get_server_info( $this->dbh );
                } else {
                        $server_info = mysql_get_server_info( $this->dbh );
                }
                return preg_replace( '/[^0-9.].*/', '', $server_info );
        }
}