Allow to select which columns to use when doing a search query

[petitphp]

Currently, there is no way of specifying which columns will be searched by a WP_Query when using the search parameter (s). The query will look for the terms in post_title, post_content and post_excerpt columns.

To restrict the search to specific columns, we can either manipulate the SQL clauses using the available hooks or write a custom SQL query. This is not practical, and it can lead to incorrect or unoptimized results.

This ticket proposes to add a new parameter search_columns to the WP_Query where we can choose which columns will be searched :

<?php
// Searching on post title
$q = new WP_Query(
    array(
        's' => 'the quick brown fox',
        'search_columns' => ['post_title'],
    )
);

// Searching on post title and excerpt
$q = new WP_Query(
    array(
        's' => 'the quick brown fox',
        'search_columns' => ['post_title', 'post_excerpt'],
    )
);

This new parameter takes an array of columns' names, with only the existing columns allowed as values (post_title, post_content and post_excerpt).

Trac ticket: https://core.trac.wordpress.org/ticket/56880

[johnbillion]

Related / dupliadte: #43867

[petitphp]

Duplicate of #43867.