sqlite-integration/query.class.php

<?php
/**
 * This file defines PDOSQLiteDriver class.
 *
 * @package SQLite Integration
 * @author  Kojima Toshiyasu
 */

/**
 * This class is for rewriting various query string except CREATE and ALTER.
 *
 */
class PDOSQLiteDriver {

	/**
	 * Variable to indicate the query types.
	 *
	 * @var string $query_type
	 */
	public $query_type = '';
	/**
	 * Variable to store query string.
	 *
	 * @var string
	 */
	public $_query = '';
	/**
	 * Variable to check if rewriting CALC_FOUND_ROWS is needed.
	 *
	 * @var boolean
	 */
	private $rewrite_calc_found = false;
	/**
	 * Variable to check if rewriting ON DUPLICATE KEY UPDATE is needed.
	 *
	 * @var boolean
	 */
	private $rewrite_duplicate_key = false;
	/**
	 * Variable to check if rewriting index hints is needed.
	 *
	 * @var boolean
	 */
	private $rewrite_index_hint = false;
	/**
	 * Variable to check if rewriting BETWEEN is needed.
	 *
	 * @var boolean
	 */
	private $rewrite_between = false;
	/**
	 * Variable to check how many times rewriting BETWEEN is needed.
	 *
	 * @var integer
	 */
	private $num_of_rewrite_between = 0;
	/**
	 * Variable to check order by field() with column data.
	 *
	 * @var boolean
	 */
	private $orderby_field = false;
	/**
	 * Method to rewrite a query string for SQLite to execute.
	 *
	 * @param strin $query
	 * @param string $query_type
	 * @return string
	 */
	public function rewrite_query($query, $query_type){
		$this->query_type = $query_type;
		$this->_query = $query;
		$this->parse_query();
		switch ($this->query_type) {
			case 'truncate':
				$this->handle_truncate_query();
				break;
			case 'alter':
				$this->handle_alter_query();
				break;
			case 'create':
				$this->handle_create_query();
				break;
			case 'describe':
			case 'desc':
				$this->handle_describe_query();
				break;
			case 'show':
				$this->handle_show_query();
				break;
			case 'showcolumns':
				$this->handle_show_columns_query();
				break;
			case 'showindex':
				$this->handle_show_index();
				break;
			case 'select':
				//$this->strip_backticks();
				$this->handle_sql_count();
				$this->rewrite_date_sub();
				$this->delete_index_hints();
				$this->rewrite_regexp();
				//$this->rewrite_boolean();
				$this->fix_date_quoting();
				$this->rewrite_between();
				$this->handle_orderby_field();
				break;
			case 'insert':
				//$this->safe_strip_backticks();
				$this->execute_duplicate_key_update();
				$this->rewrite_insert_ignore();
				$this->rewrite_regexp();
				$this->fix_date_quoting();
				break;
			case 'update':
				//$this->safe_strip_backticks();
				$this->rewrite_update_ignore();
				//$this->_rewrite_date_sub();
				$this->rewrite_limit_usage();
				$this->rewrite_order_by_usage();
				$this->rewrite_regexp();
				$this->rewrite_between();
				break;
			case 'delete':
				//$this->strip_backticks();
				$this->rewrite_limit_usage();
				$this->rewrite_order_by_usage();
				$this->rewrite_date_sub();
				$this->rewrite_regexp();
				$this->delete_workaround();
				break;
			case 'replace':
				//$this->safe_strip_backticks();
				$this->rewrite_date_sub();
				$this->rewrite_regexp();
				break;
			case 'optimize':
				$this->rewrite_optimize();
				break;
			case 'pragma':
				break;
			default:
				if (defined(WP_DEBUG) && WP_DEBUG) {
					break;
				} else {
					$this->return_true();
					break;
				}
		}
		return $this->_query;
	}

	/**
	 * Method to parse query string and determine which operation is needed.
	 *
	 * Remove backticks and change true/false values into 1/0. And determines
	 * if rewriting CALC_FOUND_ROWS or ON DUPLICATE KEY UPDATE etc is needed.
	 *
	 * @access private
	 */
	private function parse_query() {
		$tokens = preg_split("/(\\\'|''|')/s", $this->_query, -1, PREG_SPLIT_DELIM_CAPTURE);
		$literal = false;
		$query_string = '';
		foreach ($tokens as $token) {
			if ($token == "'") {
				if ($literal) {
					$literal = false;
				} else {
					$literal = true;
				}
			} else {
				if ($literal === false) {
					if (strpos($token, '`') !== false) {
						$token = str_replace('`', '', $token);
					}
					if (preg_match('/\\bTRUE\\b/i', $token)) {
					  $token = str_ireplace('TRUE', '1', $token);
					}
					if (preg_match('/\\bFALSE\\b/i', $token)) {
					  $token = str_ireplace('FALSE', '0', $token);
					}
					if (stripos($token, 'SQL_CALC_FOUND_ROWS') !== false) {
						$this->rewrite_calc_found = true;
					}
					if (stripos($token, 'ON DUPLICATE KEY UPDATE') !== false) {
						$this->rewrite_duplicate_key = true;
					}
					if (stripos($token, 'USE INDEX') !== false) {
						$this->rewrite_index_hint = true;
					}
					if (stripos($token, 'IGNORE INDEX') !== false) {
						$this->rewrite_index_hint = true;
					}
					if (stripos($token, 'FORCE INDEX') !== false) {
						$this->rewrite_index_hint = true;
					}
					if (stripos($token, 'BETWEEN') !== false) {
						$this->rewrite_between = true;
						$this->num_of_rewrite_between++;
					}
					if (stripos($token, 'ORDER BY FIELD') !== false) {
						$this->orderby_field = true;
					}
				}
			}
			$query_string .= $token;
		}
		$this->_query = $query_string;
	}
	/**
	 * method to handle SHOW TABLES query.
	 *
	 * @access private
	 */
	private function handle_show_query(){
		$this->_query = str_ireplace(' FULL', '', $this->_query);
		$table_name = '';
		$pattern    = '/^\\s*SHOW\\s*TABLES\\s*.*?(LIKE\\s*(.*))$/im';
		if (preg_match($pattern, $this->_query, $matches)) {
			$table_name = str_replace(array("'", ';'), '', $matches[2]);
		}
		if (!empty($table_name)) {
			$suffix = ' AND name LIKE '. "'" . $table_name . "'";
		} else {
			$suffix = '';
		}
		$this->_query = "SELECT name FROM sqlite_master WHERE type='table'" . $suffix . ' ORDER BY name DESC';
	}
	/**
	 * Method to strip all column qualifiers (backticks) from a query.
	 *
	 * All the back quotes in the query string are removed automatically.
	 * So it must not be used when INSERT, UPDATE or REPLACE query is executed.
	 *
	 * Obsolite since 1.5.1
	 *
	 * @access private
	 */
	private function strip_backticks(){
		$this->_query = str_replace('`', '', $this->_query);
	}
	/**
	 * Method to strip all column qualifiers (backticks) from a query except post data.
	 *
	 * All the back quotes execpt user data to be inserted are revomved automatically.
	 * This method must be used when INSERT, UPDATE or REPLACE query is executed.
	 *
	 * Obsolite since 1.5.1
	 *
	 * @access private
	 */
	private function safe_strip_backticks() {
		$query_string = '';
		$tokens       = preg_split("/(''|')/s", $this->_query, -1, PREG_SPLIT_DELIM_CAPTURE);
		$literal      = false;
		$query_string = '';
		foreach ($tokens as $token) {
			if ($token == "'") {
				if ($literal) {
					$literal = false;
				} else {
					$literal = true;
				}
			} else {
				if ($literal === false && strpos($token, '`') !== false) {
					$token = str_replace('`', '', $token);
				}
			}
			$query_string .= $token;
		}
		$this->_query = $query_string;
	}
	/**
	 * Method to emulate the SQL_CALC_FOUND_ROWS placeholder for MySQL.
	 *
	 * This is a kind of tricky play.
	 * 1. remove SQL_CALC_FOUND_ROWS option, and give it to the pdo engine
	 * 2. make another $wpdb instance, and execute the rewritten query
	 * 3. give the returned value (integer: number of the rows) to the original instance variable without LIMIT
	 *
	 * We no longer use SELECT COUNT query, because it returns the inexact values when used with WP_Meta_Query().
	 *
	 * This kind of statement is required for WordPress to calculate the paging information.
	 * see also WP_Query class in wp-includes/query.php
	 *
	 * @access private
	 */
	private function handle_sql_count(){
		if (!$this->rewrite_calc_found) return;
		global $wpdb;
		// first strip the code. this is the end of rewriting process
		$this->_query    = str_ireplace('SQL_CALC_FOUND_ROWS', '', $this->_query);
		// we make the data for next SELECE FOUND_ROWS() statement
		$unlimited_query = preg_replace('/\\bLIMIT\\s*.*/imsx', '', $this->_query);
		//$unlimited_query = preg_replace('/\\bGROUP\\s*BY\\s*.*/imsx', '', $unlimited_query);
		// we no longer use SELECT COUNT query
		//$unlimited_query = $this->_transform_to_count($unlimited_query);
		$_wpdb = new PDODB();
		$result = $_wpdb->query($unlimited_query);
		$wpdb->dbh->found_rows_result = $result;
		$_wpdb = null;
	}
	/**
	 * Call back method to change SELECT query to SELECT COUNT().
	 *
	 * obsolite since version 1.5.1
	 *
	 * @param	string $query	the query to be transformed
	 * @return string the transformed query
	 * @access private
	 */
	private function _transform_to_count($query){
		$pattern = '/^\\s*SELECT\\s*(DISTINCT|)?.*?FROM\b/isx';
		$_query = preg_replace($pattern, 'SELECT \\1 COUNT(*) FROM ', $query);
		return $_query;
	}
	/**
	 * Method to rewrite INSERT IGNORE to INSERT OR IGNORE.
	 *
	 * @access private
	 */
	private function rewrite_insert_ignore(){
		$this->_query = str_ireplace('INSERT IGNORE', 'INSERT OR IGNORE ', $this->_query);
	}
	/**
	 * Method to rewrite UPDATE IGNORE to UPDATE OR IGNORE.
	 *
	 * @access private
	 */
	private function rewrite_update_ignore(){
		$this->_query = str_ireplace('UPDATE IGNORE', 'UPDATE OR IGNORE ', $this->_query);
	}
	/**
	 * Method to rewrite DATE_ADD() function.
	 *
	 * DATE_ADD has a parameter PHP function can't parse, so we quote the list and
	 * pass it to the user defined function.
	 *
	 * @access private
	 */
	private function rewrite_date_add(){
		//(date,interval expression unit)
		$pattern = '/\\s*date_add\\s*\(([^,]*),([^\)]*)\)/imsx';
		if (preg_match($pattern, $this->_query, $matches)) {
			$expression   = "'".trim($matches[2])."'";
			$this->_query = preg_replace($pattern, " date_add($matches[1], $expression) ", $this->_query);
		}
	}
	/**
	 * Method to rewrite DATE_SUB() function.
	 *
	 * DATE_SUB has a parameter PHP function can't parse, so we quote the list and
	 * pass it to the user defined function.
	 *
	 * @access private
	 */
	private function rewrite_date_sub(){
		//(date,interval expression unit)
		$pattern = '/\\s*date_sub\\s*\(([^,]*),([^\)]*)\)/imsx';
		if (preg_match($pattern, $this->_query, $matches)) {
			$expression   = "'".trim($matches[2])."'";
			$this->_query = preg_replace($pattern, " date_sub($matches[1], $expression) ", $this->_query);
		}
	}
	/**
	 * Method to handle CREATE query.
	 *
	 * If the query is CREATE query, it will be passed to the query_create.class.php.
	 * So this method can't be used. It's here for safety.
	 *
	 * @access private
	 */
	private function handle_create_query(){
		require_once PDODIR . 'query_create.class.php';
		$engine = new CreateQuery();
		$this->_query = $engine->rewrite_query($this->_query);
		$engine = null;
	}

	/**
	 * Method to handle ALTER query.
	 *
	 * If the query is ALTER query, it will be passed ot the query_alter.class.php.
	 * So this method can't be used. It is here for safety.
	 *
	 * @access private
	 */
	private function handle_alter_query(){
		require_once PDODIR . 'query_alter.class.php';
		$engine = new AlterQuery();
		$this->_query = $engine->rewrite_query($this->_query, 'alter');
		$engine = null;
	}

	/**
	 * Method to handle DESCRIBE or DESC query.
	 *
	 * DESCRIBE is required for WordPress installation process. DESC is
	 * an alias for DESCRIBE, but it is not used in core WordPress.
	 *
	 * @access private
	 */
	private function handle_describe_query(){
		$pattern = '/^\\s*(DESCRIBE|DESC)\\s*(.*)/i';
		if (preg_match($pattern, $this->_query, $match)) {
			$tablename = preg_replace('/[\';]/', '', $match[2]);
			$this->_query = "PRAGMA table_info($tablename)";
		}
	}
	/**
	 * Method to remove LIMIT clause from DELETE or UPDATE query.
	 *
	 * The author of the original 'PDO for WordPress' says update method of wpdb
	 * insists on adding LIMIT. But the newest version of WordPress doesn't do that.
	 * Nevertheless some plugins use DELETE with LIMIT, UPDATE with LIMIT.
	 * We need to exclude sub query's LIMIT. And if SQLite is compiled with
	 * ENABLE_UPDATE_DELETE_LIMIT option, we don't remove it.
	 *
	 * @access private
	 */
	private function rewrite_limit_usage(){
		$_wpdb = new PDODB();
		$options = $_wpdb->get_results('PRAGMA compile_options');
		foreach ($options as $opt) {
			if (stripos($opt->compile_option, 'ENABLE_UPDATE_DELETE_LIMIT') !== false) return;
		}
		if (stripos($this->_query, '(select') === false) {
			$this->_query = preg_replace('/\\s*LIMIT\\s*[0-9]$/i', '', $this->_query);
		}
	}
	/**
	 * Method to remove ORDER BY clause from DELETE or UPDATE query.
	 *
	 * SQLite compiled without SQLITE_ENABLE_UPDATE_DELETE_LIMIT option can't
	 * execute UPDATE with ORDER BY, DELETE with GROUP BY.
	 * We need to exclude sub query's GROUP BY.
	 *
	 * @access private
	 */
	private function rewrite_order_by_usage() {
		$_wpdb = new PDODB();
		$options = $_wpdb->get_results('PRAGMA compile_options');
		foreach ($options as $opt) {
			if (stripos($opt->compile_option, 'ENABLE_UPDATE_DELETE_LIMIT') !== false) return;
		}
		if (stripos($this->_query, '(select') === false) {
			$this->_query = preg_replace('/\\s+ORDER\\s+BY\\s*.*$/i', '', $this->_query);
		}
	}
	/**
	 * Method to handle TRUNCATE query.
	 *
	 * @access private
	 */
	private function handle_truncate_query(){
		$pattern = '/TRUNCATE TABLE (.*)/im';
		$this->_query = preg_replace($pattern, 'DELETE FROM $1', $this->_query);
	}
	/**
	 * Method to handle OPTIMIZE query.
	 *
	 * Original query has the table names, but they are simply ignored.
	 * Table names are meaningless in SQLite.
	 *
	 * @access private
	 */
	private function rewrite_optimize(){
		$this->_query ="VACUUM";
	}
	/**
	 * Method to rewrite day.
	 *
	 * Jusitn Adie says: some wp UI interfaces (notably the post interface)
	 * badly composes the day part of the date leading to problems in sqlite
	 * sort ordering etc.
	 *
	 * I don't understand that...
	 *
	 * @return void
	 * @access private
	 */
	private function rewrite_badly_formed_dates(){
		$pattern = '/([12]\d{3,}-\d{2}-)(\d )/ims';
		$this->_query = preg_replace($pattern, '${1}0$2', $this->_query);
	}
	/**
	 * Method to remove INDEX HINT.
	 *
	 * @return void
	 * @access private
	 */
	private function delete_index_hints(){
		$pattern = '/\\s*(use|ignore|force)\\s+index\\s*\(.*?\)/i';
		$this->_query = preg_replace($pattern, '', $this->_query);
	}
	/**
	 * Method to fix the date string and quoting.
	 *
	 * This is required for the calendar widget.
	 *
	 * WHERE month(fieldname)=08 is converted to month(fieldname)='8'
	 * WHERE month(fieldname)='08' is converted to month(fieldname)='8'
	 *
	 * I use preg_replace_callback instead of 'e' option because of security reason.
	 * cf. PHP manual (regular expression)
	 *
	 * @return void
	 * @access private
	 */
	private function fix_date_quoting() {
		$pattern = '/(month|year|second|day|minute|hour|dayofmonth)\\s*\((.*?)\)\\s*=\\s*["\']?(\d{1,4})[\'"]?\\s*/im';
		$this->_query = preg_replace_callback($pattern, array($this, '_fix_date_quoting'), $this->_query);
	}
	/**
	 * Call back method to rewrite date string.
	 *
	 * @param string $match
	 * @return string
	 * @access private
	 */
	private function _fix_date_quoting($match) {
		$fixed_val = "{$match[1]}({$match[2]})='" . intval($match[3]) . "' ";
		return $fixed_val;
	}
	/**
	 * Method to rewrite REGEXP() function.
	 *
	 * This method changes function name to regexpp() and pass it to the user defined
	 * function.
	 *
	 * @access private
	 */
	private function rewrite_regexp(){
		$pattern = '/\s([^\s]*)\s*regexp\s*(\'.*?\')/im';
		$this->_query = preg_replace($pattern, ' regexpp(\1, \2)', $this->_query);
	}
	/**
	 * Method to rewrite boolean to number.
	 *
	 * SQLite doesn't support true/false type, so we need to convert them to 1/0.
	 *
	 * Obsolite since 1.5.1
	 *
	 * @access private
	 */
	private function rewrite_boolean() {
		$query = str_ireplace('TRUE', "1", $this->_query);
		$query = str_ireplace('FALSE', "0", $query);
		$this->_query = $query;
	}
	/**
	 * Method to handl SHOW COLUMN query.
	 *
	 * @access private
	 */
	private function handle_show_columns_query() {
		$this->_query = str_ireplace(' FULL', '', $this->_query);
		$pattern_like = '/^\\s*SHOW\\s*(COLUMNS|FIELDS)\\s*FROM\\s*(.*)?\\s*LIKE\\s*(.*)?/i';
		$pattern      = '/^\\s*SHOW\\s*(COLUMNS|FIELDS)\\s*FROM\\s*(.*)?/i';
		if (preg_match($pattern_like, $this->_query, $matches)) {
			$table_name   = str_replace("'", "", trim($matches[2]));
			$column_name  = str_replace("'", "", trim($matches[3]));
			$query_string = "SELECT sql FROM sqlite_master WHERE tbl_name='$table_name' AND sql LIKE '%$column_name%'";
			$this->_query = $query_string;
		} elseif (preg_match($pattern, $this->_query, $matches)) {
			$table_name   = $matches[2];
			$query_string = preg_replace($pattern, "PRAGMA table_info($table_name)", $this->_query);
			$this->_query = $query_string;
		}
	}
	/**
	 * Method to handle SHOW INDEX query.
	 *
	 * Moved the WHERE clause manipulation to pdoengin.class.php (ver 1.3.1)
	 *
	 * @access private
	 */
	private function handle_show_index() {
		$pattern = '/^\\s*SHOW\\s*(?:INDEX|INDEXES|KEYS)\\s*FROM\\s*(\\w+)?/im';
		if (preg_match($pattern, $this->_query, $match)) {
			$table_name   = preg_replace("/[\';]/", '', $match[1]);
			$table_name   = trim($table_name);
			$this->_query = "SELECT * FROM sqlite_master WHERE tbl_name='$table_name'";
		}
	}
	/**
	 * Method to handle ON DUPLICATE KEY UPDATE statement.
	 *
	 * First we use SELECT query and check if INSERT is allowed or not.
	 * Rewriting procedure looks like a detour, but I've got no other ways.
	 *
	 * Added the literal check since the version 1.5.1.
	 *
	 * @return void
	 * @access private
	 */
	private function execute_duplicate_key_update() {
		if (!$this->rewrite_duplicate_key) return;
		$unique_keys_for_cond  = array();
		$unique_keys_for_check = array();
		$pattern =  '/^\\s*INSERT\\s*INTO\\s*(\\w+)?\\s*(.*)\\s*ON\\s*DUPLICATE\\s*KEY\\s*UPDATE\\s*(.*)$/ims';
		if (preg_match($pattern, $this->_query, $match_0)) {
			$table_name  = trim($match_0[1]);
			$insert_data = trim($match_0[2]);
			$update_data = trim($match_0[3]);
			// prepare two unique key data for the table
			// 1. array('col1', 'col2, col3', etc) 2. array('col1', 'col2', 'col3', etc)
			$_wpdb = new PDODB();
			$indexes = $_wpdb->get_results("SHOW INDEX FROM {$table_name}");
			if (!empty($indexes)) {
			  foreach ($indexes as $index) {
			    if ($index->Non_unique == 0) {
			      $unique_keys_for_cond[] = $index->Column_name;
			      if (strpos($index->Column_name, ',') !== false) {
			        $unique_keys_for_check = array_merge($unique_keys_for_check, explode(',', $index->Column_name));
			      } else {
			        $unique_keys_for_check[] = $index->Column_name;
			      }
			    }
			  }
			  $unique_keys_for_check = array_map('trim', $unique_keys_for_check);
			} else {
			  // Without unique key or primary key, UPDATE statement will affect all the rows!
			  $query        = 'INSERT INTO '.$table_name.' '.$insert_data;
			  $this->_query = $query;
			  $_wpdb = null;
			  return;
			}
			// data check
			if (preg_match('/^\((.*)\)\\s*VALUES\\s*\((.*)\)$/ims', $insert_data, $match_1)) {
				$col_array      = explode(',', $match_1[1]);
				$ins_data_array = explode(',', $match_1[2]);
				foreach ($col_array as $col) {
					$val = trim(array_shift($ins_data_array));
					$ins_data_assoc[trim($col)] = $val;
				}
				$condition = '';
				foreach ($unique_keys_for_cond as $unique_key) {
					if (strpos($unique_key, ',') !== false) {
						$unique_key_array = explode(',', $unique_key);
						$counter          = count($unique_key_array);
						for ($i = 0; $i < $counter; ++$i) {
							$col = trim($unique_key_array[$i]);
							if (isset($ins_data_assoc[$col]) && $i == $counter - 1) {
								$condition .= $col . '=' . $ins_data_assoc[$col] . ' OR ';
							} elseif (isset($ins_data_assoc[$col])) {
								$condition .= $col . '=' . $ins_data_assoc[$col] . ' AND ';
							} else {
								continue;
							}
						}
					} else {
						$col = trim($unique_key);
						if (isset($ins_data_assoc[$col])) {
							$condition .= $col . '=' . $ins_data_assoc[$col] . ' OR ';
						} else {
							continue;
						}
					}
				}
				$condition  = rtrim($condition, ' OR ');
				$test_query = "SELECT * FROM {$table_name} WHERE {$condition}";
				$results    = $_wpdb->query($test_query);
				$_wpdb = null;
				if ($results == 0) {
					$this->_query = 'INSERT INTO '.$table_name.' '.$insert_data;
					return;
				} else {
					if (preg_match('/^\((.*)\)\\s*VALUES\\s*\((.*)\)$/im', $insert_data, $match_2)) {
						$col_array = explode(',', $match_2[1]);
						$ins_array = explode(',', $match_2[2]);
						$count     = count($col_array);
						for ($i = 0; $i < $count; $i++) {
							$col = trim($col_array[$i]);
							$val = trim($ins_array[$i]);
							$ins_array_assoc[$col] = $val;
						}
					}
					$update_data = rtrim($update_data, ';');
					$tmp_array   = explode(',', $update_data);
					foreach ($tmp_array as $pair) {
						list($col, $value) = explode('=', $pair);
						$col   = trim($col);
						$value = trim($value);
						$update_array_assoc[$col] = $value;
					}
					foreach ($update_array_assoc as $key => &$value) {
						if (preg_match('/^VALUES\\s*\((.*)\)$/im', $value, $match_3)) {
							$col   = trim($match_3[1]);
							$value = $ins_array_assoc[$col];
						}
					}
					foreach ($ins_array_assoc as $key => $val) {
						if (in_array($key, $unique_keys_for_check)) {
							$where_array[] = $key . '=' . $val;
						}
					}
					$update_strings = '';
					foreach ($update_array_assoc as $key => $val) {
						if (in_array($key, $unique_keys_for_check)) {
							$where_array[] = $key . '=' . $val;
						} else {
							$update_strings .= $key . '=' . $val . ',';
						}
					}
					$update_strings = rtrim($update_strings, ',');
					$unique_where   = array_unique($where_array, SORT_REGULAR);
					$where_string   = ' WHERE ' . implode(' AND ', $unique_where);
					$update_query = 'UPDATE ' . $table_name . ' SET ' . $update_strings . $where_string;
					$this->_query = $update_query;
				}
			}
		}
	}
	/**
	 * Method to rewrite BETWEEN A AND B clause.
	 *
	 * This clause is the same form as natural language, so we have to check if it is
	 * in the data or SQL statement.
	 *
	 * @access private
	 */
	private function rewrite_between() {
		if (!$this->rewrite_between) return;
		$pattern = '/\\s*(CAST\([^\)]+?\)|[^\\s\(]*)?\\s*BETWEEN\\s*([^\\s]*)?\\s*AND\\s*([^\\s\)]*)?\\s*/ims';
		do {
			if (preg_match($pattern, $this->_query, $match)) {
				$column_name  = trim($match[1]);
				$min_value    = trim($match[2]);
				$max_value    = trim($match[3]);
				$max_value    = rtrim($max_value);
				$replacement  = " ($column_name >= $min_value AND $column_name <= $max_value)";
				$this->_query = str_ireplace($match[0], $replacement, $this->_query);
			}
			$this->num_of_rewrite_between--;
		} while ($this->num_of_rewrite_between > 0);
	}
	/**
	 * Method to handle ORDER BY FIELD() clause.
	 *
	 * When FIELD() function has column name to compare, we can't rewrite it with
	 * use defined functions. When this function detect column name in the argument,
	 * it creates another instance, does the query withuot ORDER BY clause and gives
	 * the result array sorted to the main instance.
	 *
	 * If FIELD() function doesn't have column name, it will use the user defined
	 * function. usort() function closure function to compare the items.
	 *
	 * @access private
	 */
	private function handle_orderby_field() {
		if (!$this->orderby_field) return;
		global $wpdb;
		$pattern = '/\\s+ORDER\\s+BY\\s+FIELD\\s*\(\\s*([^\)]+?)\\s*\)/i';
		if (preg_match($pattern, $this->_query, $match)) {
			global $flipped;
			$params   = explode(',', $match[1]);
			$params   = array_map('trim', $params);
			$tbl_col  = array_shift($params);
			$flipped  = array_flip($params);
			$tbl_name = substr($tbl_col, 0, strpos($tbl_col, '.'));
			$tbl_name = str_replace($wpdb->prefix, '', $tbl_name);
			if ($tbl_name && in_array($tbl_name, $wpdb->tables)) {
				$query = str_replace($match[0], '', $this->_query);
				$_wpdb = new PDODB();
				$results = $_wpdb->get_results($query);
				$_wpdb = null;
				$compare = function($a, $b) {
					global $flipped;
					return $flipped[$a->ID] - $flipped[$b->ID];
				};
				usort($results, $compare);
			}
			$wpdb->dbh->pre_ordered_results = $results;
		}
	}
	/**
	 * Method to avoid DELETE with JOIN statement.
	 *
	 * wp-admin/includes/upgrade.php contains 'DELETE ... JOIN' statement.
	 * This query can't be replaced with regular expression or udf, so we
	 * replace all the statement with another. But this query was used in
	 * the very old version of WordPress when it was upgraded. So we won't
	 * have no chance that this method should be used.
	 *
	 * @access private
	 */
	private function delete_workaround() {
		global $wpdb;
		$pattern   = "DELETE o1 FROM $wpdb->options AS o1 JOIN $wpdb->options AS o2";
		$pattern2  = "DELETE a, b FROM $wpdb->sitemeta AS a, $wpdb->sitemeta AS b";
		$rewritten = "DELETE FROM $wpdb->options WHERE option_id IN (SELECT MIN(option_id) FROM $wpdb->options GROUP BY option_name HAVING COUNT(*) > 1)";
		if (stripos($this->_query, $pattern) !== false) {
			$this->_query = $rewritten;
		} else if (stripos($this->_query, $pattern2) !== false) {
			$time = time();
			$prep_query = "SELECT a.meta_id AS aid, b.meta_id AS bid FROM $wpdb->sitemeta AS a INNER JOIN $wpdb->sitemeta AS b ON a.meta_key='_site_transient_timeout_'||substr(b.meta_key, 17) WHERE b.meta_key='_site_transient_'||substr(a.meta_key, 25) AND a.meta_value < $time";
			$_wpdb = new PDODB();
			$ids   = $_wpdb->get_results($prep_query);
			foreach ($ids as $id) {
				$ids_to_delete[] = $id->aid;
				$ids_to_delete[] = $id->bid;
			}
			$rewritten = "DELETE FROM $wpdb->sitemeta WHERE meta_id IN (".implode(',', $ids_to_delete).")";
			$this->_query = $rewritten;
		}
	}
	/**
	 * Method to suppress errors.
	 *
	 * When the query string is the one that this class can't manipulate,
	 * the query string is replaced with the one that always returns true
	 * and does nothing.
	 *
	 * @access private
	 */
	private function return_true() {
		$this->_query = 'SELECT 1=1';
	}
}
?>