WordPress/wp-includes/wp-db.php

<?php
/**
 * WordPress DB Class
 *
 * Original code from {@link http://php.justinvincent.com Justin Vincent (justin@visunet.ie)}
 *
 * @package WordPress
 * @subpackage Database
 * @since 0.71
 */

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

/**
 * @since 0.71
 */
define('OBJECT', 'OBJECT', true);

/**
 * @since {@internal Version Unknown}}
 */
define('OBJECT_K', 'OBJECT_K', false);

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

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

/**
 * WordPress Database Access Abstraction Object
 *
 * It is possible to replace this class with your own
 * by setting the $wpdb global variable in wp-content/db.php
 * file with your class. You can name it wpdb also, since
 * this file will not be included, if the other file is
 * available.
 *
 * @link http://codex.wordpress.org/Function_Reference/wpdb_Class
 *
 * @package WordPress
 * @subpackage Database
 * @since 0.71
 * @final
 */
class wpdb {

	/**
	 * Whether to show SQL/DB errors
	 *
	 * @since 0.71
	 * @access private
	 * @var bool
	 */
	var $show_errors = false;

	/**
	 * Whether to suppress errors during the DB bootstrapping.
	 *
	 * @access private
	 * @since {@internal Version Unknown}}
	 * @var bool
	 */
	var $suppress_errors = false;

	/**
	 * The last error during query.
	 *
	 * @since {@internal Version Unknown}}
	 * @var string
	 */
	var $last_error = '';

	/**
	 * Amount of queries made
	 *
	 * @since 1.2.0
	 * @access private
	 * @var int
	 */
	var $num_queries = 0;

	/**
	 * Saved result of the last query made
	 *
	 * @since 1.2.0
	 * @access private
	 * @var array
	 */
	var $last_query;

	/**
	 * Saved info on the table column
	 *
	 * @since 1.2.0
	 * @access private
	 * @var array
	 */
	var $col_info;

	/**
	 * Saved queries that were executed
	 *
	 * @since 1.5.0
	 * @access private
	 * @var array
	 */
	var $queries;

	/**
	 * 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 0.71
	 * @access private
	 * @var string
	 */
	var $prefix = '';

	/**
	 * Whether the database queries are ready to start executing.
	 *
	 * @since 2.5.0
	 * @access private
	 * @var bool
	 */
	var $ready = false;

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

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

	/**
	 * WordPress Categories table
	 *
	 * @since 1.5.0
	 * @access public
	 * @var string
	 */
	var $categories;

	/**
	 * WordPress Post to Category table
	 *
	 * @since 1.5.0
	 * @access public
	 * @var string
	 */
	var $post2cat;

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

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

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

	/**
	 * WordPress Post Metadata table
	 *
	 * @since {@internal Version Unknown}}
	 * @access public
	 * @var string
	 */
	var $postmeta;

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

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

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

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

	/**
	 * List of WordPress tables
	 *
	 * @since {@internal Version Unknown}}
	 * @access private
	 * @var array
	 */
	var $tables = array('users', 'usermeta', 'posts', 'categories', 'post2cat', 'comments', 'links', 'link2cat', 'options',
			'postmeta', 'terms', 'term_taxonomy', 'term_relationships');

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

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

	/**
	 * Connects to the database server and selects a database
	 *
	 * PHP4 compatibility layer for calling the PHP5 constructor.
	 *
	 * @uses wpdb::__construct() Passes parameters and returns result
	 * @since 0.71
	 *
	 * @param string $dbuser MySQL database user
	 * @param string $dbpassword MySQL database password
	 * @param string $dbname MySQL database name
	 * @param string $dbhost MySQL database host
	 */
	function wpdb($dbuser, $dbpassword, $dbname, $dbhost) {
		return $this->__construct($dbuser, $dbpassword, $dbname, $dbhost);
	}

	/**
	 * 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
	 *
	 * @param string $dbuser MySQL database user
	 * @param string $dbpassword MySQL database password
	 * @param string $dbname MySQL database name
	 * @param string $dbhost MySQL database host
	 */
	function __construct($dbuser, $dbpassword, $dbname, $dbhost) {
		register_shutdown_function(array(&$this, "__destruct"));

		if ( defined('WP_DEBUG') and WP_DEBUG == true )
			$this->show_errors();

		if ( defined('DB_CHARSET') )
			$this->charset = DB_CHARSET;

		if ( defined('DB_COLLATE') )
			$this->collate = DB_COLLATE;

		$this->dbh = @mysql_connect($dbhost, $dbuser, $dbpassword, true);
		if (!$this->dbh) {
			$this->bail(sprintf(/*WP_I18N_DB_CONN_ERROR*/"
<h1>Error establishing a database connection</h1>
<p>This either means that the username and password information in your <code>wp-config.php</code> file is incorrect or we can't contact the database server at <code>%s</code>. This could mean your host's database server is down.</p>
<ul>
	<li>Are you sure you have the correct username and password?</li>
	<li>Are you sure that you have typed the correct hostname?</li>
	<li>Are you sure that the database server is running?</li>
</ul>
<p>If you're unsure what these terms mean you should probably contact your host. If you still need help you can always visit the <a href='http://wordpress.org/support/'>WordPress Support Forums</a>.</p>
"/*/WP_I18N_DB_CONN_ERROR*/, $dbhost));
			return;
		}

		$this->ready = true;

		if ( $this->has_cap( 'collation' ) ) {
			$collation_query = '';
			if ( !empty($this->charset) ) {
				$collation_query = "SET NAMES '{$this->charset}'";
				if (!empty($this->collate) )
					$collation_query .= " COLLATE '{$this->collate}'";
			}

			if ( !empty($collation_query) )
				$this->query($collation_query);

		}

		$this->select($dbname);
	}

	/**
	 * PHP5 style destructor and will run when database object is destroyed.
	 *
	 * @since 2.0.8
	 *
	 * @return bool Always true
	 */
	function __destruct() {
		return true;
	}

	/**
	 * Sets the table prefix for the WordPress tables.
	 *
	 * Also allows for the CUSTOM_USER_TABLE and CUSTOM_USER_META_TABLE to
	 * override the WordPress users and usersmeta tables.
	 *
	 * @since 2.5.0
	 *
	 * @param string $prefix Alphanumeric name for the new prefix.
	 * @return string Old prefix
	 */
	function set_prefix($prefix) {

		if ( preg_match('|[^a-z0-9_]|i', $prefix) )
			return new WP_Error('invalid_db_prefix', /*WP_I18N_DB_BAD_PREFIX*/'Invalid database prefix'/*/WP_I18N_DB_BAD_PREFIX*/);

		$old_prefix = $this->prefix;
		$this->prefix = $prefix;

		foreach ( (array) $this->tables as $table )
			$this->$table = $this->prefix . $table;

		if ( defined('CUSTOM_USER_TABLE') )
			$this->users = CUSTOM_USER_TABLE;

		if ( defined('CUSTOM_USER_META_TABLE') )
			$this->usermeta = CUSTOM_USER_META_TABLE;

		return $old_prefix;
	}

	/**
	 * Selects a database using the current database connection.
	 *
	 * The database name will be changed based on the current database
	 * connection. On failure, the execution will bail and display an DB error.
	 *
	 * @since 0.71
	 *
	 * @param string $db MySQL database name
	 * @return null Always null.
	 */
	function select($db) {
		if (!@mysql_select_db($db, $this->dbh)) {
			$this->ready = false;
			$this->bail(sprintf(/*WP_I18N_DB_SELECT_DB*/'
<h1>Can&#8217;t select database</h1>
<p>We were able to connect to the database server (which means your username and password is okay) but not able to select the <code>%1$s</code> database.</p>
<ul>
<li>Are you sure it exists?</li>
<li>Does the user <code>%2$s</code> have permission to use the <code>%1$s</code> database?</li>
<li>On some systems the name of your database is prefixed with your username, so it would be like username_wordpress. Could that be the problem?</li>
</ul>
<p>If you don\'t know how to setup a database you should <strong>contact your host</strong>. If all else fails you may find help at the <a href="http://wordpress.org/support/">WordPress Support Forums</a>.</p>'/*/WP_I18N_DB_SELECT_DB*/, $db, DB_USER));
			return;
		}
	}

	/**
	 * Escapes content for insertion into the database, for security
	 *
	 * @since 0.71
	 *
	 * @param string $string
	 * @return string query safe string
	 */
	function escape($string) {
		return addslashes( $string );
		// Disable rest for now, causing problems
		/*
		if( !$this->dbh || version_compare( phpversion(), '4.3.0' ) == '-1' )
			return mysql_escape_string( $string );
		else
			return mysql_real_escape_string( $string, $this->dbh );
		*/
	}

	/**
	 * Escapes content by reference for insertion into the database, for security
	 *
	 * @since 2.3.0
	 *
	 * @param string $s
	 */
	function escape_by_ref(&$s) {
		$s = $this->escape($s);
	}

	/**
	 * Prepares a SQL query for safe use, using sprintf() syntax.
	 *
	 * @link http://php.net/sprintf See for syntax to use for query string.
	 * @since 2.3.0
	 *
	 * @param null|string $args If string, first parameter must be query statement
	 * @param mixed $args,... If additional parameters, they will be set inserted into the query.
	 * @return null|string Sanitized query string
	 */
	function prepare($args=null) {
		if ( is_null( $args ) )
			return;
		$args = func_get_args();
		$query = array_shift($args);
		$query = str_replace("'%s'", '%s', $query); // in case someone mistakenly already singlequoted it
		$query = str_replace('"%s"', '%s', $query); // doublequote unquoting
		$query = str_replace('%s', "'%s'", $query); // quote the strings
		array_walk($args, array(&$this, 'escape_by_ref'));
		return @vsprintf($query, $args);
	}

	/**
	 * Print SQL/DB error.
	 *
	 * @since 0.71
	 * @global array $EZSQL_ERROR Stores error information of query and error string
	 *
	 * @param string $str The error to display
	 * @return bool False if the showing of errors is disabled.
	 */
	function print_error($str = '') {
		global $EZSQL_ERROR;

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

		if ( $this->suppress_errors )
			return false;

		if ( $caller = $this->get_caller() )
			$error_str = sprintf(/*WP_I18N_DB_QUERY_ERROR_FULL*/'WordPress database error %1$s for query %2$s made by %3$s'/*/WP_I18N_DB_QUERY_ERROR_FULL*/, $str, $this->last_query, $caller);
		else
			$error_str = sprintf(/*WP_I18N_DB_QUERY_ERROR*/'WordPress database error %1$s for query %2$s'/*/WP_I18N_DB_QUERY_ERROR*/, $str, $this->last_query);

		$log_error = true;
		if ( ! function_exists('error_log') )
			$log_error = false;

		$log_file = @ini_get('error_log');
		if ( !empty($log_file) && ('syslog' != $log_file) && !is_writable($log_file) )
			$log_error = false;

		if ( $log_error )
			@error_log($error_str, 0);

		// Is error output turned on or not..
		if ( !$this->show_errors )
			return false;

		$str = htmlspecialchars($str, ENT_QUOTES);
		$query = htmlspecialchars($this->last_query, ENT_QUOTES);

		// If there is an error then take note of it
		print "<div id='error'>
		<p class='wpdberror'><strong>WordPress database error:</strong> [$str]<br />
		<code>$query</code></p>
		</div>";
	}

	/**
	 * Enables showing of database errors.
	 *
	 * This function should be used only to enable showing of errors.
	 * wpdb::hide_errors() should be used instead for hiding of errors. However,
	 * this function can be used to enable and disable showing of database
	 * errors.
	 *
	 * @since 0.71
	 *
	 * @param bool $show Whether to show or hide errors
	 * @return bool Old value for showing errors.
	 */
	function show_errors( $show = true ) {
		$errors = $this->show_errors;
		$this->show_errors = $show;
		return $errors;
	}

	/**
	 * Disables showing of database errors.
	 *
	 * @since 0.71
	 *
	 * @return bool Whether showing of errors was active or not
	 */
	function hide_errors() {
		$show = $this->show_errors;
		$this->show_errors = false;
		return $show;
	}

	/**
	 * Whether to suppress database errors.
	 *
	 * @param unknown_type $suppress
	 * @return unknown
	 */
	function suppress_errors( $suppress = true ) {
		$errors = $this->suppress_errors;
		$this->suppress_errors = $suppress;
		return $errors;
	}

	/**
	 * Kill cached query results.
	 *
	 * @since 0.71
	 */
	function flush() {
		$this->last_result = array();
		$this->col_info = null;
		$this->last_query = null;
	}

	/**
	 * Perform a MySQL database query, using current database connection.
	 *
	 * More information can be found on the codex page.
	 *
	 * @since 0.71
	 *
	 * @param string $query
	 * @return unknown
	 */
	function query($query) {
		if ( ! $this->ready )
			return false;

		// filter the query, if filters are available
		// NOTE: some queries are made before the plugins have been loaded, and thus cannot be filtered with this method
		if ( function_exists('apply_filters') )
			$query = apply_filters('query', $query);

		// initialise return
		$return_val = 0;
		$this->flush();

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

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

		// Perform the query via std mysql_query function..
		if ( defined('SAVEQUERIES') && SAVEQUERIES )
			$this->timer_start();

		$this->result = @mysql_query($query, $this->dbh);
		++$this->num_queries;

		if ( defined('SAVEQUERIES') && SAVEQUERIES )
			$this->queries[] = array( $query, $this->timer_stop(), $this->get_caller() );

		// If there is an error then take note of it..
		if ( $this->last_error = mysql_error($this->dbh) ) {
			$this->print_error();
			return false;
		}

		if ( preg_match("/^\\s*(insert|delete|update|replace) /i",$query) ) {
			$this->rows_affected = mysql_affected_rows($this->dbh);
			// Take note of the insert_id
			if ( preg_match("/^\\s*(insert|replace) /i",$query) ) {
				$this->insert_id = mysql_insert_id($this->dbh);
			}
			// Return number of rows affected
			$return_val = $this->rows_affected;
		} else {
			$i = 0;
			while ($i < @mysql_num_fields($this->result)) {
				$this->col_info[$i] = @mysql_fetch_field($this->result);
				$i++;
			}
			$num_rows = 0;
			while ( $row = @mysql_fetch_object($this->result) ) {
				$this->last_result[$num_rows] = $row;
				$num_rows++;
			}

			@mysql_free_result($this->result);

			// Log number of rows the query returned
			$this->num_rows = $num_rows;

			// Return number of rows selected
			$return_val = $this->num_rows;
		}

		return $return_val;
	}

	/**
	 * Insert an array of data into a table.
	 *
	 * @since 2.5.0
	 *
	 * @param string $table WARNING: not sanitized!
	 * @param array $data Should not already be SQL-escaped
	 * @return mixed Results of $this->query()
	 */
	function insert($table, $data) {
		$data = add_magic_quotes($data);
		$fields = array_keys($data);
		return $this->query("INSERT INTO $table (`" . implode('`,`',$fields) . "`) VALUES ('".implode("','",$data)."')");
	}

	/**
	 * Update a row in the table with an array of data.
	 *
	 * @since 2.5.0
	 *
	 * @param string $table WARNING: not sanitized!
	 * @param array $data Should not already be SQL-escaped
	 * @param array $where A named array of WHERE column => value relationships.  Multiple member pairs will be joined with ANDs.  WARNING: the column names are not currently sanitized!
	 * @return mixed Results of $this->query()
	 */
	function update($table, $data, $where){
		$data = add_magic_quotes($data);
		$bits = $wheres = array();
		foreach ( (array) array_keys($data) as $k )
			$bits[] = "`$k` = '$data[$k]'";

		if ( is_array( $where ) )
			foreach ( $where as $c => $v )
				$wheres[] = "$c = '" . $this->escape( $v ) . "'";
		else
			return false;

		return $this->query( "UPDATE $table SET " . implode( ', ', $bits ) . ' WHERE ' . implode( ' AND ', $wheres ) );
	}

	/**
	 * Retrieve one variable from the database.
	 *
	 * This combines the functionality of wpdb::get_row() and wpdb::get_col(),
	 * so both the column and row can be picked.
	 *
	 * It is possible to use this function without executing more queries. If
	 * you already made a query, you can set the $query to 'null' value and just
	 * retrieve either the column and row of the last query result.
	 *
	 * @since 0.71
	 *
	 * @param string $query Can be null as well, for caching
	 * @param int $x Column num to return
	 * @param int $y Row num to return
	 * @return mixed Database query results
	 */
	function get_var($query=null, $x = 0, $y = 0) {
		$this->func_call = "\$db->get_var(\"$query\",$x,$y)";
		if ( $query )
			$this->query($query);

		// Extract var out of cached results based x,y vals
		if ( !empty( $this->last_result[$y] ) ) {
			$values = array_values(get_object_vars($this->last_result[$y]));
		}

		// If there is a value return it else return null
		return (isset($values[$x]) && $values[$x]!=='') ? $values[$x] : null;
	}

	/**
	 * Retrieve one row from the database.
	 *
	 * @since 0.71
	 *
	 * @param string $query SQL query
	 * @param string $output ARRAY_A | ARRAY_N | OBJECT
	 * @param int $y Row num to return
	 * @return mixed Database query results
	 */
	function get_row($query = null, $output = OBJECT, $y = 0) {
		$this->func_call = "\$db->get_row(\"$query\",$output,$y)";
		if ( $query )
			$this->query($query);
		else
			return null;

		if ( !isset($this->last_result[$y]) )
			return null;

		if ( $output == OBJECT ) {
			return $this->last_result[$y] ? $this->last_result[$y] : null;
		} elseif ( $output == ARRAY_A ) {
			return $this->last_result[$y] ? get_object_vars($this->last_result[$y]) : null;
		} elseif ( $output == ARRAY_N ) {
			return $this->last_result[$y] ? array_values(get_object_vars($this->last_result[$y])) : null;
		} else {
			$this->print_error(/*WP_I18N_DB_GETROW_ERROR*/" \$db->get_row(string query, output type, int offset) -- Output type must be one of: OBJECT, ARRAY_A, ARRAY_N"/*/WP_I18N_DB_GETROW_ERROR*/);
		}
	}

	/**
	 * Retrieve one column from the database.
	 *
	 * @since 0.71
	 *
	 * @param string $query Can be null as well, for caching
	 * @param int $x Col num to return. Starts from 0.
	 * @return array Column results
	 */
	function get_col($query = null , $x = 0) {
		if ( $query )
			$this->query($query);

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

	/**
	 * Retrieve an entire result set from the database.
	 *
	 * @since 0.71
	 *
	 * @param string|null $query Can also be null to pull from the cache
	 * @param string $output ARRAY_A | ARRAY_N | OBJECT_K | OBJECT
	 * @return mixed Database query results
	 */
	function get_results($query = null, $output = OBJECT) {
		$this->func_call = "\$db->get_results(\"$query\", $output)";

		if ( $query )
			$this->query($query);
		else
			return null;

		if ( $output == OBJECT ) {
			// Return an integer-keyed array of row objects
			return $this->last_result;
		} elseif ( $output == OBJECT_K ) {
			// Return an array of row objects with keys from column 1
			// (Duplicates are discarded)
			foreach ( $this->last_result as $row ) {
				$key = array_shift( get_object_vars( $row ) );
				if ( !isset( $new_array[ $key ] ) )
					$new_array[ $key ] = $row;
			}
			return $new_array;
		} elseif ( $output == ARRAY_A || $output == ARRAY_N ) {
			// Return an integer-keyed array of...
			if ( $this->last_result ) {
				$i = 0;
				foreach( (array) $this->last_result as $row ) {
					if ( $output == ARRAY_N ) {
						// ...integer-keyed row arrays
						$new_array[$i] = array_values( get_object_vars( $row ) );
					} else {
						// ...column name-keyed row arrays
						$new_array[$i] = get_object_vars( $row );
					}
					++$i;
				}
				return $new_array;
			}
		}
	}

	/**
	 * Retrieve column metadata from the last query.
	 *
	 * @since 0.71
	 *
	 * @param string $info_type one of name, table, def, max_length, not_null, primary_key, multiple_key, unique_key, numeric, blob, type, unsigned, zerofill
	 * @param int $col_offset 0: col name. 1: which table the col's in. 2: col's max length. 3: if the col is numeric. 4: col's type
	 * @return mixed Column Results
	 */
	function get_col_info($info_type = 'name', $col_offset = -1) {
		if ( $this->col_info ) {
			if ( $col_offset == -1 ) {
				$i = 0;
				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 bool Always returns true
	 */
	function timer_start() {
		$mtime = microtime();
		$mtime = explode(' ', $mtime);
		$this->time_start = $mtime[1] + $mtime[0];
		return true;
	}

	/**
	 * Stops the debugging timer.
	 *
	 * @since 1.5.0
	 *
	 * @return int Total time spent on the query, in milliseconds
	 */
	function timer_stop() {
		$mtime = microtime();
		$mtime = explode(' ', $mtime);
		$time_end = $mtime[1] + $mtime[0];
		$time_total = $time_end - $this->time_start;
		return $time_total;
	}

	/**
	 * Wraps fatal errors in a nice header and footer and dies.
	 *
	 * @since 1.5.0
	 *
	 * @param string $message
	 * @return unknown
	 */
	function bail($message) {
		if ( !$this->show_errors ) {
			if ( class_exists('WP_Error') )
				$this->error = new WP_Error('500', $message);
			else
				$this->error = $message;
			return false;
		}
		wp_die($message);
	}

	/**
	 * Whether or not MySQL database is minimal required version.
	 *
	 * @since 2.5.0
	 * @uses $wp_version
	 *
	 * @return WP_Error
	 */
	function check_database_version()
	{
		global $wp_version;
		// Make sure the server has MySQL 4.0
		if ( version_compare($this->db_version(), '4.0.0', '<') )
			return new WP_Error('database_version',sprintf(__('<strong>ERROR</strong>: WordPress %s requires MySQL 4.0.0 or higher'), $wp_version));
	}

	/**
	 * Whether of not the database version supports collation.
	 *
	 * Called when WordPress is generating the table scheme.
	 *
	 * @since 2.5.0
	 *
	 * @return bool True if collation is supported, false if version does not
	 */
	function supports_collation()
	{
		return $this->has_cap( 'collation' );
	}

	/**
	 * Generic function to determine if a database supports a particular feature
	 * @param string $db_cap the feature
	 * @param false|string|resource $dbh_or_table the databaese (the current database, the database housing the specified table, or the database of the mysql resource)
	 * @return bool
	 */
	function has_cap( $db_cap ) {
		$version = $this->db_version();

		switch ( strtolower( $db_cap ) ) :
		case 'collation' :    // @since 2.5.0
		case 'group_concat' : // @since 2.7
		case 'subqueries' :   // @since 2.7
			return version_compare($version, '4.1', '>=');
			break;
		endswitch;

		return false;
	}

	/**
	 * Retrieve the name of the function that called wpdb.
	 *
	 * Requires PHP 4.3 and 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 The name of the calling function
	 */
	function get_caller() {
		// requires PHP 4.3+
		if ( !is_callable('debug_backtrace') )
			return '';

		$bt = debug_backtrace();
		$caller = '';

		foreach ( (array) $bt as $trace ) {
			if ( @$trace['class'] == __CLASS__ )
				continue;
			elseif ( strtolower(@$trace['function']) == 'call_user_func_array' )
				continue;
			elseif ( strtolower(@$trace['function']) == 'apply_filters' )
				continue;
			elseif ( strtolower(@$trace['function']) == 'do_action' )
				continue;

			$caller = $trace['function'];
			break;
		}
		return $caller;
	}

	/**
	 * The database version number
	 * @return false|string false on failure, version number on success
	 */
	function db_version() {
		return preg_replace('/[^0-9.].*/', '', mysql_get_server_info( $this->dbh ));
	}
}

if ( ! isset($wpdb) ) {
	/**
	 * WordPress Database Object, if it isn't set already in wp-content/db.php
	 * @global object $wpdb Creates a new wpdb object based on wp-config.php Constants for the database
	 * @since 0.71
	 */
	$wpdb = new wpdb(DB_USER, DB_PASSWORD, DB_NAME, DB_HOST);
}
?>