wpdb

WordPress Database Access Abstraction Object


Description Description

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.


Source Source

File: wp-includes/wp-db.php

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;

	/**
	 * 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.
		 */
		$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 );
	}
}

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Changelog Changelog

Changelog
Version Description
0.71 Introduced.

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Methods Methods

  • __construct — Connects to the database server and selects a database
  • __destruct — PHP5 style destructor and will run when database object is destroyed.
  • __get — Makes private properties readable for backward compatibility.
  • __isset — Makes private properties check-able for backward compatibility.
  • __set — Makes private properties settable for backward compatibility.
  • __unset — Makes private properties un-settable for backward compatibility.
  • _do_query — Internal function to perform the mysql_query() call.
  • _escape — Escape data. Works on arrays.
  • _insert_replace_helper — Helper function for insert and replace.
  • _real_escape — Real escape, using mysqli_real_escape_string() or mysql_real_escape_string()
  • _weak_escape — Do not use, deprecated. — deprecated
  • add_placeholder_escape — Adds a placeholder escape string, to escape anything that resembles a printf() placeholder.
  • bail — Wraps errors in a nice header and footer and dies.
  • check_ascii — Check if a string is ASCII.
  • check_connection — Checks that the connection to the database is still up. If not, try to reconnect.
  • check_database_version — Whether MySQL database is at least the required minimum version.
  • check_safe_collation — Check if the query is accessing a collation considered safe on the current version of MySQL.
  • close — Closes the current database connection.
  • db_connect — Connect to and select database.
  • db_version — Retrieves the MySQL server version.
  • delete — Delete a row in the table
  • determine_charset — Determines the best charset and collation to use given a charset and collation.
  • esc_like — First half of escaping for LIKE special characters % and _ before preparing for MySQL.
  • escape — Do not use, deprecated. — deprecated
  • escape_by_ref — Escapes content by reference for insertion into the database, for security
  • flush — Kill cached query results.
  • get_blog_prefix — Gets blog prefix.
  • get_caller — Retrieve the name of the function that called wpdb.
  • get_charset_collate — The database character collate.
  • get_col — Retrieve one column from the database.
  • get_col_charset — Retrieves the character set for the given column.
  • get_col_info — Retrieve column metadata from the last query.
  • get_col_length — Retrieve the maximum string length allowed in a given column.
  • get_results — Retrieve an entire SQL result set from the database (i.e., many rows)
  • get_row — Retrieve one row from the database.
  • get_table_charset — Retrieves the character set for the given table.
  • get_table_from_query — Find the first table name referenced in a query.
  • get_var — Retrieve one variable from the database.
  • has_cap — Determine if a database supports a particular feature.
  • hide_errors — Disables showing of database errors.
  • init_charset — Set $this->charset and $this->collate
  • insert — Insert a row into a table.
  • load_col_info — Load the column metadata from the last query.
  • log_query — Logs query data.
  • parse_db_host — Parse the DB_HOST setting to interpret it for mysqli_real_connect.
  • placeholder_escape — Generates and returns a placeholder escape string for use in queries returned by ::prepare().
  • prepare — Prepares a SQL query for safe execution. Uses sprintf()-like syntax.
  • print_error — Print SQL/DB error.
  • process_field_charsets — Adds field charsets to field/value/format arrays generated by the wpdb::process_field_formats() method.
  • process_field_formats — Prepares arrays of value/format pairs as passed to wpdb CRUD methods.
  • process_field_lengths — For string fields, record the maximum string length that field can safely save.
  • process_fields — Processes arrays of field/value pairs and field formats.
  • query — Perform a MySQL database query, using current database connection.
  • remove_placeholder_escape — Removes the placeholder escape strings from a query.
  • replace — Replace a row into a table.
  • select — Selects a database using the current database connection.
  • set_blog_id — Sets blog id.
  • set_charset — Sets the connection's character set.
  • set_prefix — Sets the table prefix for the WordPress tables.
  • set_sql_mode — Change the current SQL mode, and ensure its WordPress compatibility.
  • show_errors — Enables showing of database errors.
  • strip_invalid_text — Strips any invalid characters based on value/charset pairs.
  • strip_invalid_text_for_column — Strips any invalid characters from the string for a given table and column.
  • strip_invalid_text_from_query — Strips any invalid characters from the query.
  • supports_collation — Whether the database supports collation. — deprecated
  • suppress_errors — Whether to suppress database errors.
  • tables — Returns an array of WordPress tables.
  • timer_start — Starts the timer, for debugging purposes.
  • timer_stop — Stops the debugging timer.
  • update — Update a row in the table

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User Contributed Notes User Contributed Notes

  1. Skip to note 1 content
    Contributed by Priyanka Behera

    Retrieve and display the sum of a Custom Field value.

    // set the meta_key to the appropriate custom field meta key
    $meta_key = 'miles';
    $allmiles = $wpdb->get_var( $wpdb->prepare( 
    	"
    		SELECT sum(meta_value) 
    		FROM $wpdb->postmeta 
    		WHERE meta_key = %s
    	", 
    	$meta_key
    ) );
    echo "<p>Total miles is {$allmiles}</p>";
    
    
  2. Skip to note 3 content
    Contributed by Aurovrata Venet

    These page is missing quite a lot of additional information relative to the older codex page.
    The global $wpdb instance can access the following variables,

    Class Variables

    • $show_errors Whether or not Error echoing is turned on. Defaults to TRUE.
    • $num_queries The number of queries that have been executed.
    • $last_query The most recent query to have been executed.
    • $last_error The most recent error text generated by MySQL.
    • $queries You may save all of the queries run on the database and their stop times by setting the SAVEQUERIES constant to TRUE (this constant defaults to FALSE). If SAVEQUERIES is TRUE, your queries will be stored in this variable as an array.
    • $last_result The most recent query results.
    • $col_info The column information for the most recent query results. See Getting Column Information.
    • $insert_id ID generated for an AUTO_INCREMENT column by the most recent INSERT query.
    • $num_rows The number of rows returned by the last query.
    • $prefix The assigned WordPress table prefix for the site.
    • $base_prefix The original prefix as defined in wp-config.php. For multi-site: Use if you want to get the prefix without the blog number appended.

    Multi-Site Variables

    If you are using Multi-Site, you also have access to the following:

    Tables

    The WordPress database tables are easily referenced in the wpdb class.

    • $posts The table of Posts.
    • $postmeta The Meta Content (a.k.a. Custom Fields) table.
    • $comments The Comments table.
    • $commentmeta The table contains additional comment information.
    • $termmeta The termmeta table contains the term meta values.
    • $terms The terms table contains the ‘description’ of Categories, Link Categories, Tags.
    • $term_taxonomy The term_taxonomy table describes the various taxonomies (classes of terms). Categories, Link Categories, and Tags are taxonomies.
    • $term_relationships The term relationships table contains link between the term and the object that uses that term, meaning this file point to each Category used for each Post.
    • $users The table of Users.
    • $usermeta The usermeta table contains additional user information, such as nicknames, descriptions and permissions.
    • $links The table of Links.
    • $options The Options table.

    Multisite Tables

    These tables are used only in multisite installations.

    • $blogs The Blogs table contains a list of the separate blogs (sites) that have been set up within the network(s).
    • $blogmeta The Blogmeta table is used to store data associated with a particulate blog in multisite context. See more info in this blog post.
    • $signups The Signups table.
    • $site The Site table contains a list of the networks (previously known as “sites” in WPMU) that are set up in the installation (usually there is only one site listed in this table).
    • $sitemeta The Network Options (Site Meta) table contains any options that are applicable to the entire multisite installation.
    • $sitecategories The Site Categories table.
    • $registration_log The Registration Log table.
    • $blog_versions The Blog Versions table.

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