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wpdb

WordPress database access abstraction class.

Description

This class is used to interact with a database without needing to use raw SQL statements. By default, WordPress uses this class to instantiate the global $wpdb object, providing access to the WordPress database.

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.

More Information

An instantiated wpdb class can talk to any number of tables, but only to one database at a time. In the rare case you need to connect to another database, instantiate your own object from the wpdb class with your own database connection information.

Note: Each method contained within the class is listed in the Methods section (below). In addition, each method has its own help page; this is where you’ll find detailed usage information for the method you’re interested in.

An Important Note Regarding Escaping

Some of the methods in this class take an SQL statement as input. All untrusted values in an SQL statement must be escaped to prevent SQL injection attacks. Some methods will escape SQL for you; others will not. Check the documentation to be sure before you use any method in this class. For more on SQL escaping in WordPress, see the section entitled Protect Queries Against SQL Injection Attacks below.

Using the `$wpdb` global object

WordPress provides a global object, $wpdb, which is an instantiation of the wpdb class. By default, $wpdb is instantiated to talk to the WordPress database.

The recommended way to access $wpdb in your WordPress PHP code is to declare $wpdb as a global variable using the global keyword, like this:

<?php
// 1st Method - Declaring $wpdb as global and using it to execute an SQL query statement that returns a PHP object
global $wpdb;
$results = $wpdb->get_results( "SELECT * FROM {$wpdb->prefix}options WHERE option_id = 1", OBJECT );

Alternatively, if the above doesn’t suit your needs for whatever reason, use the superglobal $GLOBALS in the following manner:

<?php
// 2nd Method - Utilizing the $GLOBALS superglobal. Does not require global keyword ( but may not be best practice )
$results = $GLOBALS['wpdb']->get_results( "SELECT * FROM {$wpdb->prefix}options WHERE option_id = 1", OBJECT );

The $wpdb object can be used to read data from any table in the WordPress database, not just those created by WordPress itself.

Protect Queries Against SQL Injection Attacks

For a more complete overview of SQL escaping in WordPress, see database Data Validation. It is a must-read for all WordPress code contributors and plugin authors.

All data in SQL queries must be SQL-escaped before the SQL query is executed to prevent against SQL injection attacks. The prepare method performs this functionality for WordPress, which supports both a sprintf()-like and vsprintf()-like syntax.

Using it looks like this:

<?php
$sql = $wpdb->prepare( 'query' , value_parameter[, value_parameter ... ] );

query: (string) The SQL query you wish to execute, with placeholders (see below).
value_parameter: (int|string|array) The value to substitute into the placeholder. Many values may be passed by simply passing more arguments in a sprintf()-like fashion. Alternatively the second argument can be an array containing the values as in PHP’s vsprintf() function. Care must be taken not to allow direct user input to this parameter, which would enable array manipulation of any query with multiple placeholders.Note: Values cannot be SQL-escaped.

Placeholders

The query parameter for prepare accepts sprintf()-like placeholders:

%s (string)
%d (integer)
%f (float)

Notes on placeholders

Any other % characters may cause parsing errors unless they are escaped.
All % characters inside SQL string literals, including LIKE wildcards, must be double-% escaped as %%.
Leave %d, %f, and %s unquoted in the query string.

Examples

Add Meta key => value pair “Funny Phrases” => “WordPress’ database interface is like Sunday Morning: Easy.” to Post 10.

<?php
$metakey   = 'Funny Phrases';
$metavalue = "WordPress' database interface is like Sunday Morning: Easy.";

</pre>
<pre>$wpdb->query(
   $wpdb->prepare(
      "
      INSERT INTO $wpdb->postmeta
      ( post_id, meta_key, meta_value )
      VALUES ( %d, %s, %s )
      ",
      10,
      $metakey,
      $metavalue
   )
);

The same query using vsprintf()-like syntax. Note that in this example we pack the values together in an array. This can be useful when we don’t know the number of arguments we need to pass until runtime.

<?php
$metakey   = 'Funny Phrases';
$metavalue = "WordPress' database interface is like Sunday Morning: Easy.";

$wpdb->query(
   $wpdb->prepare(
   "
   INSERT INTO $wpdb->postmeta
   ( post_id, meta_key, meta_value )
   VALUES ( %d, %s, %s )
   ",
   array(
         10,
         $metakey,
         $metavalue,
      )
   )
);

In both cases, we do not need to escape the strings because we are passing them using placeholders. You can pass as many values as you like, provided each one has a corresponding placeholder in the prepare() method call.

Common Tasks

Each of the class’s properties and methods are listed below, and most have their own help page that you should consult for detailed usage information. This section, however, gives an overview of some of the more common tasks this class can be used to perform.

SELECT a Variable

The get_var function returns a single variable from the database. Though only one variable is returned, the entire result of the query is cached for later use. Returns NULL if no result is found.

 <?php $wpdb->get_var( 'query', column_offset, row_offset ); ?>

query: (string) The query you wish to run. Setting this parameter to null will return the specified variable from the cached results of the previous query.
column_offset: (integer) The desired column (0 being the first). Defaults to 0.
row_offset: (integer) The desired row (0 being the first). Defaults to 0.

Examples

Retrieve and display the number of users.

<?php
$user_count = $wpdb->get_var( "SELECT COUNT(*) FROM $wpdb->users" );
echo "<p>User count is {$user_count}</p>";
?>

Retrieve and display the sum of a Custom Field value.

<?php
// set the meta_key to the appropriate custom field meta key
$meta_key = 'miles';
$allmiles = $wpdb->get_var(
	$wpdb->prepare(
		"
			SELECT sum(meta_value)
			FROM $wpdb->postmeta
			WHERE meta_key = %s
		",
		$meta_key
	)
);
echo "<p>Total miles is {$allmiles}</p>";
?>

SELECT a Row

To retrieve an entire row from a query, use get_row. The function can return the row as an object, an associative array, or as a numerically indexed array. If more than one row is returned by the query, only the specified row is returned by the function, but all rows are cached for later use. Returns null if no result is found, consider this when using the returned value in arguments, see example below.

<?php $wpdb->get_row('query', output_type, row_offset); ?>

query: (string) The query you wish to run.
output_type: One of three pre-defined constants. Defaults to OBJECT.

OBJECT – result will be output as an object.
ARRAY_A – result will be output as an associative array.
ARRAY_N – result will be output as a numerically indexed array.

row_offset: (integer) The desired row (0 being the first). Defaults to 0.

Examples

Get all the information about Link 10.

$mylink = $wpdb->get_row( "SELECT * FROM $wpdb->links WHERE link_id = 10" );

The properties of the <code>$mylink</code> object are the column names of the result from the SQL query (in this example all the columns from the <code>$wpdb->links</code> table, but you could also query for specific columns only).

echo $mylink->link_id; // prints "10"

In contrast, using

$mylink = $wpdb->get_row( "SELECT * FROM $wpdb->links WHERE link_id = 10", ARRAY_A );

would result in an associative array:

echo $mylink['link_id']; // prints "10"

and

$mylink = $wpdb->get_row( "SELECT * FROM $wpdb->links WHERE link_id = 10", ARRAY_N );

would result in a numerically indexed array:

echo $mylink[1]; // prints "10"

If there is no record with ID 10 in the links table, null will be returned. The following would then be false:

if ( null !== $mylink ) {
  // do something with the link 
  return true;
} else {
  // no link found
  return false;
}

SELECT a Column

To SELECT a column, use get_col. This method outputs a one dimensional array. If more than one column is returned by the query, only the specified column will be returned, but the entire result is cached for later use. Returns an empty array if no result is found.

get_col( 'query', column_offset ); ?>

query: (string) the query you wish to execute. Setting this parameter to null will return the specified column from the cached results of the previous query.
column_offset: (integer) The desired column (0 being the first). Defaults to 0.

Examples

For this example, assume the blog is devoted to information about automobiles. Each post describes a particular car (e.g. 1969 Ford Mustang), and three Custom Fields, manufacturer, model, and year, are assigned to each post. This example will display the post titles, filtered by a particular manufacturer (Ford), and sorted by model and year.

The get_col method is used to return an array of all the post ids meeting the criteria and sorted in the correct order. Then a foreach construct is used to iterate through that array of post ids, displaying the title of each post. Note that the SQL for this example was created by Andomar.

<?php 
$meta_key1       = 'model';
$meta_key2       = 'year';
$meta_key3       = 'manufacturer';
$meta_key3_value = 'Ford';

$postids = $wpdb->get_col( $wpdb->prepare( 
	"
		SELECT      key3.post_id
		FROM        $wpdb->postmeta key3
		INNER JOIN  $wpdb->postmeta key1 
	            ON key1.post_id = key3.post_id
	            AND key1.meta_key = %s 
		INNER JOIN  $wpdb->postmeta key2
	            ON key2.post_id = key3.post_id
	            AND key2.meta_key = %s
		WHERE       key3.meta_key = %s 
	            AND key3.meta_value = %s
		ORDER BY    key1.meta_value, key2.meta_value
	",
	$meta_key1, 
	$meta_key2, 
	$meta_key3, 
	$meta_key3_value
) ); 

if ( $postids ) {
	echo "List of {$meta_key3_value}(s), sorted by {$meta_key1}, {$meta_key2}";
	foreach ( $postids as $id ) { 
		$post = get_post( intval( $id ) );
		setup_postdata( $post );
		?>
		<p>
			<a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>">
				<?php the_title(); ?>
			</a>
		</p>
		<?php
	} 
}
?>

This example lists all posts that contain a particular custom field, but sorted by the value of a second custom field.

<?php
// List all posts with custom field Color, sorted by the value of custom field Display_Order
// does not exclude any 'post_type'
// assumes each post has just one custom field for Color, and one for Display_Order
$meta_key1 = 'Color';
$meta_key2 = 'Display_Order';

$postids = $wpdb->get_col( $wpdb->prepare( 
	"
		SELECT      key1.post_id
		FROM        $wpdb->postmeta key1
		INNER JOIN  $wpdb->postmeta key2
	            ON key2.post_id = key1.post_id
	            AND key2.meta_key = %s
		WHERE       key1.meta_key = %s
		ORDER BY    key2.meta_value+(0) ASC
	",
        $meta_key2,
	$meta_key1
) ); 

if ( $postids ) {
	echo "List of {$meta_key1} posts, sorted by {$meta_key2}";
	foreach ( $postids as $id ) {
		$post = get_post( intval( $id ) );
		setup_postdata( $post );
		?>
		<p>
			<a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>">
				<?php the_title(); ?>
			</a>
		</p>
		<?php
	}
}
?>

SELECT Generic Results

Generic, multiple row results can be pulled from the database with get_results. The method returns the entire query result as an array. Each element of this array corresponds to one row of the query result and, like get_row, can be an object, an associative array, or a numbered array. If no matching rows are found, or if there is a database error, the return value will be an empty array. If your $query string is empty, or you pass an invalid $output_type, NULL will be returned.

get_results( 'query', output_type );

query

(string) The query you wish to run.

output_type

One of four pre-defined constants. Defaults to OBJECT. See SELECT a Row and its examples for more information.

OBJECT – result will be output as a numerically indexed array of row objects.
OBJECT_K – result will be output as an associative array of row objects, using first column’s values as keys (duplicates will be discarded).
ARRAY_A – result will be output as a numerically indexed array of associative arrays, using column names as keys.
ARRAY_N – result will be output as a numerically indexed array of numerically indexed arrays.

Since this method uses the $wpdb->query() method, all the class variables are properly set. The results count for a ‘SELECT’ query will be stored in $wpdb->num_rows.

Examples

Get the IDs and Titles of all the Drafts by User 5 and echo the Titles.

$fivesdrafts = $wpdb->get_results( 
	"
		SELECT ID, post_title 
		FROM $wpdb->posts
		WHERE post_status = 'draft' 
		AND post_author = 5
	"
);

foreach ( $fivesdrafts as $fivesdraft ) {
	echo $fivesdraft->post_title;
}

Get all information on the Drafts by User 5.

<?php
$fivesdrafts = $wpdb->get_results( 
	"
		SELECT * 
		FROM $wpdb->posts
		WHERE post_status = 'draft' 
		AND post_author = 5
	"
);

if ( $fivesdrafts ) {
	foreach ( $fivesdrafts as $post ) {
		setup_postdata( $post );
		?>
		<h2>
			<a href="<?php the_permalink(); ?>" rel="bookmark" title="Permalink: <?php the_title(); ?>">
				<?php the_title(); ?>
			</a>
		</h2>
		<?php
	}	
} else {
	?>
	<h2>Not Found</h2>
	<?php
}
?>

INSERT row

The insert method is used to insert a row into a table.

insert( $table, $data, $format );

$table: (string) The name of the table to insert data into.
$data: (array) Data to insert (in column => value pairs). Both $data columns and $data values should be “raw” (neither should be SQL escaped).
$format: (array|string) (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. If omitted, all values in $data will be treated as strings unless otherwise specified in wpdb::$field_types.

Possible format values: %s as string; %d as integer (whole number); and %f as float. (See below for more information.)

Note: After insert, the ID generated for the AUTO_INCREMENT column can be accessed with:

$wpdb->insert_id

This method returns false if the row could not be inserted. Otherwise, it returns the number of affected rows (which will always be 1).

Please note: The value portion of the data parameter’s column=>value pairs must be scalar. If you pass an array (or object) as a value to be inserted you will generate a warning.

Examples

Insert two columns in a row, the first value being a string and the second a number:

$wpdb->insert( 
	'table', 
	array( 
		'column1' => 'value1', 
		'column2' => 123, 
	), 
	array( 
		'%s', 
		'%d', 
	) 
);

REPLACE row

The replace method replaces a row in a table if it exists or inserts a new row in a table if the row did not already exist.

replace( $table, $data, $format );

$table: (string) The name of the table to replace data in.
$data: (array) Data to replace (in column => value pairs). Both $data columns and $data values should be “raw” (neither should be SQL escaped).
$format: (array|string) (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. If omitted, all values in $data will be treated as strings unless otherwise specified in wpdb::$field_types. Possible format values: %s as string; %d as integer (whole number); and %f as float. (See below for more information.)

If the length of a string element in the $data array parameter is longer that the defined length in the MySql database table, the insert will fail, this method will return false, but $wpdb->last_error will not be set to a descriptive message. You must ensure the data you wish to insert will fit in the database – do not assume the MySql will truncate the data.

After replace, the ID generated for the AUTO_INCREMENT column can be accessed with:

$wpdb->insert_id

This method returns a count to indicate the number of rows affected. This is the sum of the rows deleted and inserted. If the count is 1 for a single-row REPLACE, a row was inserted and no rows were deleted. If the count is greater than 1, one or more old rows were deleted before the new row was inserted. It is possible for a single row to replace more than one old row if the table contains multiple unique indexes and the new row duplicates values for different old rows in different unique indexes.

This method returns false if an existing row could not be replaced and a new row could not be inserted.

Examples

Replace a row, the first value being the row id, the second a string and the third a number:

$wpdb->replace( 
	'table', 
	array( 
                'indexed_id' => 1,
		'column1' => 'value1', 
		'column2' => 123, 
	), 
	array( 
                '%d',
		'%s', 
		'%d', 
	) 
);

UPDATE rows

Update a row in the table. Returns false if errors, or the number of rows affected if successful. (wpdb::update)

update( $table, $data, $where, $format = null, $where_format = null );

$table: (string) The name of the table to update.
$data: (array) Data to update (in column => value pairs). Both $data columns and $data values should be “raw” (neither should be SQL escaped). This means that if you are using GET or POST data you may need to use stripslashes() to avoid slashes ending up in the database.
$where: (array) 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”.
$format: (array|string) (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.
$where_format: (array|string) (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. Possible format values: %s as string; %d as integer (whole number) and %f as float. (See below for more information.) If omitted, all values in $where will be treated as strings.

This method returns the number of rows updated, or false if there is an error. Keep in mind that if the $data matches what is already in the database, no rows will be updated, so 0 will be returned. Because of this, you should probably check the return with false === $result

Examples

Update a row, where the ID is 1, the value in the first column is a string and the value in the second column is a number:

$wpdb->update( 
	'table', 
	array( 
		'column1' => 'value1',	// string
		'column2' => 'value2'	// integer (number) 
	), 
	array( 'ID' => 1 ), 
	array( 
		'%s',	// value1
		'%d'	// value2
	), 
	array( '%d' ) 
);

Attention: %d can’t deal with comma values – if you’re not using full numbers, use string/%s.

DELETE Rows

The delete method is used to delete rows from a table. The usage is very similar to update and insert. It returns the number of rows updated, or false on error.

delete( $table, $where, $where_format = null );

$table: (string) (required) Table name.Default: None
$where: (array) (required) 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’. Default: None
$where_format: (string/array) (optional) An array of formats to be mapped to each of the values in $where. If a string, that format will be used for all of the items in $where. A format is one of '%d', '%f', '%s' (integer, float, string; see below for more information). If omitted, all values in $where will be treated as strings unless otherwise specified in wpdb::$field_types. Default: null

Examples

// Default usage.
$wpdb->delete( 'table', array( 'ID' => 1 ) );

// Using where formatting.
$wpdb->delete( 'table', array( 'ID' => 1 ), array( '%d' ) );

Running General Queries

The query method allows you to execute any SQL query on the WordPress database. It is best used when there is a need for specific, custom, or otherwise complex SQL queries. For more basic queries, such as selecting information from a table, see the other wpdb methods above such as get_results, get_var, get_row or get_col.

query('query');

query: (string) The SQL query you wish to execute.

This method returns an integer value indicating the number of rows affected/selected for SELECT, INSERT, DELETE, UPDATE, etc. For CREATE, ALTER, TRUNCATE and DROP SQL statements, (which affect whole tables instead of specific rows) this method returns TRUE on success. If a MySQL error is encountered, the method will return FALSE. Note that since both 0 and FALSE may be returned for row queries, you should be careful when checking the return value. Use the identity operator (===) to check for errors (e.g., false === $result), and whether any rows were affected (e.g., 0 === $result).

Examples

Delete the ‘gargle’ meta key and value from Post 13. (We’ll add the ‘prepare’ method to make sure we’re not dealing with an illegal operation or any illegal characters):

$wpdb->query( 
	$wpdb->prepare( 
		"
                	DELETE FROM $wpdb->postmeta
			WHERE post_id = %d
			AND meta_key = %s
		",
	        13, 'gargle' 
        )
);

Set the parent of Page 15 to Page 7.

$wpdb->query( $wpdb->prepare( 
	"
		UPDATE $wpdb->posts 
		SET post_parent = %d
		WHERE ID = %d
		AND post_status = %s
	",
        7, 15, 'static'
) );

Show and Hide SQL Errors

You can turn error echoing on and off with the show_errors and hide_errors, respectively.

<?php $wpdb->show_errors(); ?> 
<?php $wpdb->hide_errors(); ?>

You can also print the error (if any) generated by the most recent query with print_error.

<?php $wpdb->print_error(); ?>

Note: If you are running WordPress Multisite, you must define the DIEONDBERROR constant for database errors to display like so:

<?php define( 'DIEONDBERROR', true ); ?>

Getting Column Information

You can retrieve information about the columns of the most recent query result with get_col_info. This can be useful when a function has returned an OBJECT whose properties you don’t know. The function will output the desired information from the specified column, or an array with information on all columns from the query result if no column is specified.

<?php $wpdb->get_col_info('type', offset); ?>

type
(string) What information you wish to retrieve. May take on any of the following values (list taken from the ezSQL docs). Defaults to name.

name – column name. Default.
table – name of the table the column belongs to
max_length – maximum length of the column
not_null – 1 if the column cannot be NULL
primary_key – 1 if the column is a primary key
unique_key – 1 if the column is a unique key
multiple_key – 1 if the column is a non-unique key
numeric – 1 if the column is numeric
blob – 1 if the column is a BLOB
type – the type of the column
unsigned – 1 if the column is unsigned
zerofill – 1 if the column is zero-filled

offset
(integer) Specify the column from which to retrieve information (with 0 being the first column). Defaults to -1.

-1 – Retrieve information from all columns. Output as array. Default.
Non-negative integer – Retrieve information from specified column (0 being the first).

Clearing the Cache

You can clear the SQL result cache with flush.

<?php $wpdb->flush(); ?>

This clears $wpdb->last_result, $wpdb->last_query, and $wpdb->col_info.

Tables

The tables that WordPress creates by default can be found here.

Properties

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

Multi-Site Variables

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

$blogid — The id of the current site (blog).
$siteid — The id of the current network (formerly “site”). WordPress currently only supports one network per multi-site install, but that could change in future. See the following for more information: WordPress: difference between site_id and blog_id?
http://stackoverflow.com/a/4189358/1924128 – Another good answer to the same question.

Tables

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

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

Multisite Tables

These tables are used only in multisite installations.

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

For more information about the tables WordPress creates and uses, look here.

Source

File: wp-includes/wp-db.php

class wpdb {

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

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

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

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

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

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

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

	/**
	 * The last query made.
	 *
	 * @since 0.71
	 * @var string
	 */
	var $last_query;

	/**
	 * Results of the last query.
	 *
	 * @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. Default false.
	 *
	 * @since 4.2.0
	 * @var bool
	 */
	protected $check_current_query = true;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	//
	// Global and Multisite tables
	//

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	/**
	 * Whether to use mysqli over mysql. Default false.
	 *
	 * @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.
	 *
	 * @since 2.0.8
	 *
	 * @link https://core.trac.wordpress.org/ticket/3354
	 * @global string $wp_version The WordPress version string.
	 *
	 * @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 ) {
		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();
	}

	/**
	 * 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 );
	}

	/**
	 * Sets $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.
	 *
	 *     @type string $charset Character set.
	 *     @type string $collate Collation.
	 * }
	 */
	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 );
				}
			}
		}
	}

	/**
	 * Changes the current SQL mode, and ensures 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. Default empty array.
	 */
	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, true ) ) {
				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. Default true.
	 * @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 $scope argument can take one of the following:
	 *
	 * 'all' - returns 'all' and 'global' tables. No old tables are returned.
	 * 'blog' - returns the blog-level tables for the queried blog.
	 * 'global' - returns the global tables for the installation, returning multisite tables only on multisite.
	 * 'ms_global' - returns the multisite global tables, regardless if current installation is multisite.
	 * 'old' - returns tables which are deprecated.
	 *
	 * @since 3.0.0
	 *
	 * @uses wpdb::$tables
	 * @uses wpdb::$old_tables
	 * @uses wpdb::$global_tables
	 * @uses wpdb::$ms_global_tables
	 *
	 * @param string $scope   Optional. Possible values include 'all', 'global', 'ms_global', 'blog',
	 *                        or 'old' tables. Default 'all'.
	 * @param bool   $prefix  Optional. Whether to include table prefixes. If blog prefix is requested,
	 *                        then the custom users and usermeta tables will be mapped. Default true.
	 * @param int    $blog_id Optional. The blog_id to prefix. Used only when prefix is requested.
	 *                        Defaults to wpdb::$blogid.
	 * @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, true ) ) {
					$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 a DB error.
	 *
	 * @since 0.71
	 *
	 * @param string        $db  MySQL database name.
	 * @param resource|null $dbh Optional link identifier.
	 */
	public function select( $db, $dbh = null ) {
		if ( is_null( $dbh ) ) {
			$dbh = $this->dbh;
		}

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

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

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

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

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

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

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

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

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

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

	/**
	 * Real escape, using mysqli_real_escape_string() or mysql_real_escape_string().
	 *
	 * @since 2.8.0
	 *
	 * @see mysqli_real_escape_string()
	 * @see mysql_real_escape_string()
	 *
	 * @param string $string String to escape.
	 * @return string Escaped string.
	 */
	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 );
	}

	/**
	 * Escapes data. Works on arrays.
	 *
	 * @since 2.8.0
	 *
	 * @uses wpdb::_real_escape()
	 *
	 * @param string|array $data Data to escape.
	 * @return string|array Escaped data, in the same type as supplied.
	 */
	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 string|array $data Data to escape.
	 * @return string|array Escaped data, in the same type as supplied.
	 */
	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 $string String to escape.
	 */
	public function escape_by_ref( &$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.
	 *
	 * Note: There is one exception to the above: 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.
	 *
	 * Literal percentage signs (%) in the query string must be written as %%. Percentage wildcards
	 * (for example, to use in LIKE syntax) must be passed via a substitution argument containing
	 * the complete LIKE string, these cannot be inserted directly in the query string.
	 * Also see wpdb::esc_like().
	 *
	 * Arguments may be passed as individual arguments to the method, or as a single array
	 * containing all arguments. A combination of the two is not supported.
	 *
	 * Examples:
	 *     $wpdb->prepare( "SELECT * FROM `table` WHERE `column` = %s AND `field` = %d OR `other_field` LIKE %s", array( 'foo', 1337, '%bar' ) );
	 *     $wpdb->prepare( "SELECT DATE_FORMAT(`field`, '%%c') FROM `table` WHERE `column` = %s", 'foo' );
	 *
	 * @since 2.3.0
	 * @since 5.3.0 Formalized the existing and already documented `...$args` parameter
	 *              by updating the function signature. The second parameter was changed
	 *              from `$args` to `...$args`.
	 *
	 * @link https://www.php.net/sprintf Description of syntax.
	 *
	 * @param string      $query   Query statement with sprintf()-like placeholders.
	 * @param array|mixed $args    The array of variables to substitute into the query's placeholders
	 *                             if being called with an array of arguments, or the first variable
	 *                             to substitute into the query's placeholders if being called with
	 *                             individual arguments.
	 * @param mixed       ...$args Further variables to substitute into the query's placeholders
	 *                             if being called with individual arguments.
	 * @return string|void Sanitized query string, if there is a query to prepare.
	 */
	public function prepare( $query, ...$args ) {
		if ( is_null( $query ) ) {
			return;
		}

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

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

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

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

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

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

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

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

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

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

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

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

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

	/**
	 * Prints 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 void|false Void if the showing of errors is enabled, false if disabled.
	 */
	public function print_error( $str = '' ) {
		global $EZSQL_ERROR;

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

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

		wp_load_translations_early();

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

		error_log( $error_str );

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

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

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

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

	/**
	 * Enables showing of database errors.
	 *
	 * This function should be used only to enable showing of errors.
	 * wpdb::hide_errors() should be used instead for hiding errors.
	 *
	 * @since 0.71
	 *
	 * @see wpdb::hide_errors()
	 *
	 * @param bool $show Optional. Whether to show errors. Default true.
	 * @return bool Whether showing of errors was previously active.
	 */
	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 previously active.
	 */
	public function hide_errors() {
		$show              = $this->show_errors;
		$this->show_errors = false;
		return $show;
	}

	/**
	 * Enables or disables suppressing of database errors.
	 *
	 * By default database errors are suppressed.
	 *
	 * @since 2.5.0
	 *
	 * @see wpdb::hide_errors()
	 *
	 * @param bool $suppress Optional. Whether to suppress errors. Default true.
	 * @return bool Whether suppressing of errors was previously active.
	 */
	public function suppress_errors( $suppress = true ) {
		$errors                = $this->suppress_errors;
		$this->suppress_errors = (bool) $suppress;
		return $errors;
	}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

			$this->has_connected = true;

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

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

			return true;
		}

		return false;
	}

	/**
	 * Parses 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|false Array containing the host, the port, the socket and
	 *                     whether it is an IPv6 address, in that order.
	 *                     False if $host couldn't be parsed.
	 */
	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 ( false !== $socket_pos ) {
			$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 called
	 * after the {@see 'template_redirect'} hook has been fired, return false instead.
	 *
	 * If $allow_bail is false, the lack of database connection will need to be handled manually.
	 *
	 * @since 3.9.0
	 *
	 * @param bool $allow_bail Optional. Allows the function to bail. Default true.
	 * @return bool|void True if the connection is up.
	 */
	public function check_connection( $allow_bail = true ) {
		if ( $this->use_mysqli ) {
			if ( ! empty( $this->dbh ) && mysqli_ping( $this->dbh ) ) {
				return true;
			}
		} else {
			if ( ! empty( $this->dbh ) && mysql_ping( $this->dbh ) ) {
				return true;
			}
		}

		$error_reporting = false;

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

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

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

				return true;
			}

			sleep( 1 );
		}

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

		if ( ! $allow_bail ) {
			return false;
		}

		wp_load_translations_early();

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

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

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

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

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

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

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

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

		$this->flush();

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

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

		$this->check_current_query = true;

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

		$this->_do_query( $query );

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

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

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

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

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

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

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

		return $return_val;
	}

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

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

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

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

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

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

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

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

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

		return $placeholder;
	}

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

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

	/**
	 * Inserts a row into the table.
	 *
	 * Examples:
	 *     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' );
	}

	/**
	 * Replaces a row in the table.
	 *
	 * Examples:
	 *     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. Type of operation. Possible values include 'INSERT' or 'REPLACE'.
	 *                             Default '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' ), true ) ) {
			return false;
		}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	/**
	 * Deletes a row in the table.
	 *
	 * Examples:
	 *     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 $data will be treated as strings unless otherwise
	 *                                   specified in wpdb::$field_types.
	 * @return int|false The number of rows updated, or false on error.
	 */
	public function delete( $table, $where, $where_format = null ) {
		if ( ! is_array( $where ) ) {
			return false;
		}

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

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

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

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

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

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

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

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

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

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

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

		return $data;
	}

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

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

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

			$data[ $field ] = $value;
		}

		return $data;
	}

	/**
	 * Adds field charsets to field/value/format arrays generated by wpdb::process_field_formats().
	 *
	 * @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.
	 *                     False on failure.
	 */
	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, records 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;
	}

	/**
	 * Retrieves 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,
	 * the value in the column and row specified is returned. If $query is null,
	 * the value in the specified column and row from the previous SQL result is returned.
	 *
	 * @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 on 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;
	}

	/**
	 * Retrieves 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 ( OBJECT === $output ) {
			return $this->last_result[ $y ] ? $this->last_result[ $y ] : null;
		} elseif ( ARRAY_A === $output ) {
			return $this->last_result[ $y ] ? get_object_vars( $this->last_result[ $y ] ) : null;
		} elseif ( ARRAY_N === $output ) {
			return $this->last_result[ $y ] ? array_values( get_object_vars( $this->last_result[ $y ] ) ) : null;
		} elseif ( OBJECT === strtoupper( $output ) ) {
			// 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' );
		}
	}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	/**
	 * Retrieves 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;
		}
	}

	/**
	 * Checks 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;
	}

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

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

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

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

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

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

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

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

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

		return true;
	}

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

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

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

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

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

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

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

				if ( ! $needs_validation ) {
					continue;
				}
			}

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

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

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

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

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

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

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

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

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

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

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

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

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

		return $data;
	}

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

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

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

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

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

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

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

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

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

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

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

	/**
	 * Finds the first table name referenced in a query.
	 *
	 * @since 4.2.0
	 *
	 * @param string $query The query to search.
	 * @return string|false 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;
	}

	/**
	 * Loads 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 );
			}
		}
	}

	/**
	 * Retrieves column metadata from the last query.
	 *
	 * @since 0.71
	 *
	 * @param string $info_type  Optional. Possible values include 'name', 'table', 'def', 'max_length',
	 *                           'not_null', 'primary_key', 'multiple_key', 'unique_key', 'numeric',
	 *                           'blob', 'type', 'unsigned', 'zerofill'. Default 'name'.
	 * @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. Default -1.
	 * @return mixed Column results.
	 */
	public function get_col_info( $info_type = 'name', $col_offset = -1 ) {
		$this->load_col_info();

		if ( $this->col_info ) {
			if ( -1 === $col_offset ) {
				$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.
	 *                           Default '500'.
	 * @return void|false Void if the showing of errors is enabled, false if disabled.
	 */
	public function bail( $message, $error_code = '500' ) {
		if ( $this->show_errors ) {
			$error = '';

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

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

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

			return false;
		}
	}


	/**
	 * Closes the current database connection.
	 *
	 * @since 4.5.0
	 *
	 * @return bool True if the connection was successfully closed,
	 *              false if it wasn't, or if 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;
	}

	/**
	 * Determines whether MySQL database is at least the required minimum version.
	 *
	 * @since 2.5.0
	 *
	 * @global string $wp_version             The WordPress version string.
	 * @global string $required_mysql_version The required MySQL version string.
	 * @return void|WP_Error
	 */
	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 ) );
		}
	}

	/**
	 * Determines 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 not.
	 */
	public function supports_collation() {
		_deprecated_function( __FUNCTION__, '3.5.0', 'wpdb::has_cap( \'collation\' )' );
		return $this->has_cap( 'collation' );
	}

	/**
	 * Retrieves 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;
	}

	/**
	 * Determines 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;
	}

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

	/**
	 * Retrieves the MySQL server version.
	 *
	 * @since 2.7.0
	 *
	 * @return string|null Version number on success, null on failure.
	 */
	public function db_version() {
		return preg_replace( '/[^0-9.].*/', '', $this->db_server_info() );
	}

	/**
	 * Retrieves full MySQL server information.
	 *
	 * @since 5.5.0
	 *
	 * @return string|false Server info on success, false on failure.
	 */
	public function db_server_info() {
		if ( $this->use_mysqli ) {
			$server_info = mysqli_get_server_info( $this->dbh );
		} else {
			$server_info = mysql_get_server_info( $this->dbh );
		}

		return $server_info;
	}
}

Methods

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

Changelog

Version	Description
0.71	Introduced.

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Licensed under the GNU GPLv2+ License.
https://developer.wordpress.org/reference/classes/wpdb

wpdb

Description

More Information

An Important Note Regarding Escaping

Using the $wpdb global object

Protect Queries Against SQL Injection Attacks

Placeholders

Examples

Common Tasks

SELECT a Variable

Examples

SELECT a Row

Examples

SELECT a Column

Examples

SELECT Generic Results

Examples

INSERT row

Examples

REPLACE row

Examples

UPDATE rows

Examples

DELETE Rows

Examples

Running General Queries

Examples

Show and Hide SQL Errors

Getting Column Information

Clearing the Cache

Tables

Properties

Multi-Site Variables

Tables

Multisite Tables

Source

Methods

Changelog

Using the `$wpdb` global object