HTML Examples/WP.iso/wordpress2/wp-includes/wp-db.php

PHP Script | 2018-01-22 | 97.1 KB | 3,431 lines

<?php
/**
 * WordPress DB Class
 *
 * Original code from {@link http://php.justinvincent.com Justin Vincent ([e-mail])}
 *
 * @package WordPress
 * @subpackage Database
 * @since 0.71
 */

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

/**
 * @since 0.71
 */
define( 'OBJECT', 'OBJECT' );
define( 'object', 'OBJECT' ); // Back compat.

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

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

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

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

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

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

    /**
     * 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 array
     */
    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;

    /**
     * Saved queries that were executed
     *
     * @since 1.5.0
     * @var array
     */
    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', 'signups', 'site', 'sitemeta',
        'sitecategories', 'registration_log', 'blog_versions' );

    /**
     * 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 Versions table
     *
     * @since 3.0.0
     * @var string
     */
    public $blog_versions;

    /**
     * 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’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’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/' )
                ) . "</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 {@see 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
     *
     * @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 wih 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( __( 'The query argument of %s must have a placeholder.' ), 'wpdb::prepare()' ), '3.9.0' );
        }

        $args = func_get_args();
        array_shift( $args );

        // 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( __( '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 backwards 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',
                    /* translators: 1: number of placeholders, 2: number of arguments passed */
                    sprintf( __( '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();

        if ( $caller = $this->get_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 = $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;

            if ( $host_data = $this->parse_db_host( $this->dbhost ) ) {
                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 {
                @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 {
                $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’t contact the database server at %2$s. This could mean your host’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 that you have typed the correct hostname?' ) . "</li>\n";
            $message .= '<li>' . __( 'Are you sure that the database server is running?' ) . "</li>\n";
            $message .= "</ul>\n";

            $message .= '<p>' . sprintf(
                /* translators: %s: support forums URL */
                __( 'If you’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/' )
            ) . "</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’s database server is down.' ),
            '<code>' . htmlspecialchars( $this->dbhost, ENT_QUOTES ) . '</code>'
        ) . "</p>\n";

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

        $message .= '<p>' . sprintf(
            /* translators: %s: support forums URL */
            __( 'If you’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/' )
        ) . "</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|false Number of rows affected/selected or 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->queries[] = array( $query, $this->timer_stop(), $this->get_caller() );
        }
    }

    /**
     * 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 recieve the query with the placeholder string removed.
         */
        if ( ! 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 = $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 = $conditions = $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 = $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 = $original_formats = (array) $format;

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


    /**
     * 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|array The name of the calling function
     */
    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 );
    }
}