Ticket #32310: patch.diff

wp-admin/includes/upgrade.php

@@ -1759 +1759 @@
                 }
         }
 
-        return $wpdb->query( "ALTER TABLE $table CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci" );
+        if (_get_table_collation($table) != 'utf8mb4_unicode_ci')
+                return $wpdb->query( "ALTER TABLE $table CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci" );
+
+        return true;
 }
 
 /**
+ * Get the collation of a table utf8mb4.
+ *
+ * @since 4.2.0
+ *
+ * @param string $table The table to check.
+ * @return string like utf8mb4_unicode_ci.
+ */
+function _get_table_collation($table) {
+    global $wpdb;
+
+    $table_detail = $wpdb->get_results("show table status like '".$table."'");
+    if (empty($table_detail)) return false;
+    $table_detail = array_shift($table_detail);
+
+    return $table_detail->Collation;
+}
+
+/**
  * Retrieve all options as it was for 1.2.
  *
  * @since 1.2.0