CDbCommand.php

<?php
/**
 * This file contains the CDbCommand class.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @link http://www.yiiframework.com/
 * @copyright Copyright &copy; 2008-2011 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

/**
 * CDbCommand represents an SQL statement to execute against a database.
 *
 * It is usually created by calling {@link CDbConnection::createCommand}.
 * The SQL statement to be executed may be set via {@link setText Text}.
 *
 * To execute a non-query SQL (such as insert, delete, update), call
 * {@link execute}. To execute an SQL statement that returns result data set
 * (such as SELECT), use {@link query} or its convenient versions {@link queryRow},
 * {@link queryColumn}, or {@link queryScalar}.
 *
 * If an SQL statement returns results (such as a SELECT SQL), the results
 * can be accessed via the returned {@link CDbDataReader}.
 *
 * CDbCommand supports SQL statment preparation and parameter binding.
 * Call {@link bindParam} to bind a PHP variable to a parameter in SQL.
 * Call {@link bindValue} to bind a value to an SQL parameter.
 * When binding a parameter, the SQL statement is automatically prepared.
 * You may also call {@link prepare} to explicitly prepare an SQL statement.
 *
 * Starting from version 1.1.6, CDbCommand can also be used as a query builder
 * that builds a SQL statement from code fragments. For example,
 * <pre>
 * $user = Yii::app()->db->createCommand()
 *     ->select('username, password')
 *     ->from('tbl_user')
 *     ->where('id=:id', array(':id'=>1))
 *     ->queryRow();
 * </pre>
 *
 * @property string $text The SQL statement to be executed.
 * @property CDbConnection $connection The connection associated with this command.
 * @property PDOStatement $pdoStatement The underlying PDOStatement for this command
 * It could be null if the statement is not prepared yet.
 * @property string $select The SELECT part (without 'SELECT') in the query.
 * @property boolean $distinct A value indicating whether SELECT DISTINCT should be used.
 * @property string $from The FROM part (without 'FROM' ) in the query.
 * @property string $where The WHERE part (without 'WHERE' ) in the query.
 * @property mixed $join The join part in the query. This can be an array representing
 * multiple join fragments, or a string representing a single jojin fragment.
 * Each join fragment will contain the proper join operator (e.g. LEFT JOIN).
 * @property string $group The GROUP BY part (without 'GROUP BY' ) in the query.
 * @property string $having The HAVING part (without 'HAVING' ) in the query.
 * @property string $order The ORDER BY part (without 'ORDER BY' ) in the query.
 * @property string $limit The LIMIT part (without 'LIMIT' ) in the query.
 * @property string $offset The OFFSET part (without 'OFFSET' ) in the query.
 * @property mixed $union The UNION part (without 'UNION' ) in the query.
 * This can be either a string or an array representing multiple union parts.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @version $Id$
 * @package system.db
 * @since 1.0
 */
class CDbCommand extends CComponent
{
	/**
	 * @var array the parameters (name=>value) to be bound to the current query.
	 * @since 1.1.6
	 */
	public $params=array();

	private $_connection;
	private $_text;
	private $_statement;
	private $_paramLog=array();
	private $_query;
	private $_fetchMode = array(PDO::FETCH_ASSOC);

	/**
	 * Constructor.
	 * @param CDbConnection $connection the database connection
	 * @param mixed $query the DB query to be executed. This can be either
	 * a string representing a SQL statement, or an array whose name-value pairs
	 * will be used to set the corresponding properties of the created command object.
	 *
	 * For example, you can pass in either <code>'SELECT * FROM tbl_user'</code>
	 * or <code>array('select'=>'*', 'from'=>'tbl_user')</code>. They are equivalent
	 * in terms of the final query result.
	 *
	 * When passing the query as an array, the following properties are commonly set:
	 * {@link select}, {@link distinct}, {@link from}, {@link where}, {@link join},
	 * {@link group}, {@link having}, {@link order}, {@link limit}, {@link offset} and
	 * {@link union}. Please refer to the setter of each of these properties for details
	 * about valid property values. This feature has been available since version 1.1.6.
	 *
	 * Since 1.1.7 it is possible to use a specific mode of data fetching by setting
 	 * {@link setFetchMode FetchMode}. See {@link http://www.php.net/manual/en/function.PDOStatement-setFetchMode.php}
 	 * for more details.
	 */
	public function __construct(CDbConnection $connection,$query=null)
	{
		$this->_connection=$connection;
		if(is_array($query))
		{
			foreach($query as $name=>$value)
				$this->$name=$value;
		}
		else
			$this->setText($query);
	}

	/**
	 * Set the statement to null when serializing.
	 * @return array
	 */
	public function __sleep()
	{
		$this->_statement=null;
		return array_keys(get_object_vars($this));
	}

	/**
	 * Set the default fetch mode for this statement
	 * @param mixed $mode fetch mode
	 * @return CDbCommand
	 * @see http://www.php.net/manual/en/function.PDOStatement-setFetchMode.php
	 * @since 1.1.7
	 */
	public function setFetchMode($mode)
	{
		$params=func_get_args();
		$this->_fetchMode = $params;
		return $this;
	}

	/**
	 * Cleans up the command and prepares for building a new query.
	 * This method is mainly used when a command object is being reused
	 * multiple times for building different queries.
	 * Calling this method will clean up all internal states of the command object.
	 * @return CDbCommand this command instance
	 * @since 1.1.6
	 */
	public function reset()
	{
		$this->_text=null;
		$this->_query=null;
		$this->_statement=null;
		$this->_paramLog=array();
		$this->params=array();
		return $this;
	}

	/**
	 * @return string the SQL statement to be executed
	 */
	public function getText()
	{
		if($this->_text=='' && !empty($this->_query))
			$this->setText($this->buildQuery($this->_query));
		return $this->_text;
	}

	/**
	 * Specifies the SQL statement to be executed.
	 * Any previous execution will be terminated or cancel.
	 * @param string $value the SQL statement to be executed
	 * @return CDbCommand this command instance
	 */
	public function setText($value)
	{
		if($this->_connection->tablePrefix!==null && $value!='')
			$this->_text=preg_replace('/{{(.*?)}}/',$this->_connection->tablePrefix.'\1',$value);
		else
			$this->_text=$value;
		$this->cancel();
		return $this;
	}

	/**
	 * @return CDbConnection the connection associated with this command
	 */
	public function getConnection()
	{
		return $this->_connection;
	}

	/**
	 * @return PDOStatement the underlying PDOStatement for this command
	 * It could be null if the statement is not prepared yet.
	 */
	public function getPdoStatement()
	{
		return $this->_statement;
	}

	/**
	 * Prepares the SQL statement to be executed.
	 * For complex SQL statement that is to be executed multiple times,
	 * this may improve performance.
	 * For SQL statement with binding parameters, this method is invoked
	 * automatically.
	 */
	public function prepare()
	{
		if($this->_statement==null)
		{
			try
			{
				$this->_statement=$this->getConnection()->getPdoInstance()->prepare($this->getText());
				$this->_paramLog=array();
			}
			catch(Exception $e)
			{
				Yii::log('Error in preparing SQL: '.$this->getText(),CLogger::LEVEL_ERROR,'system.db.CDbCommand');
                $errorInfo = $e instanceof PDOException ? $e->errorInfo : null;
				throw new CDbException(Yii::t('yii','CDbCommand failed to prepare the SQL statement: {error}',
					array('{error}'=>$e->getMessage())),(int)$e->getCode(),$errorInfo);
			}
		}
	}

	/**
	 * Cancels the execution of the SQL statement.
	 */
	public function cancel()
	{
		$this->_statement=null;
	}

	/**
	 * Binds a parameter to the SQL statement to be executed.
	 * @param mixed $name Parameter identifier. For a prepared statement
	 * using named placeholders, this will be a parameter name of
	 * the form :name. For a prepared statement using question mark
	 * placeholders, this will be the 1-indexed position of the parameter.
	 * @param mixed $value Name of the PHP variable to bind to the SQL statement parameter
	 * @param integer $dataType SQL data type of the parameter. If null, the type is determined by the PHP type of the value.
	 * @param integer $length length of the data type
	 * @param mixed $driverOptions the driver-specific options (this is available since version 1.1.6)
	 * @return CDbCommand the current command being executed
	 * @see http://www.php.net/manual/en/function.PDOStatement-bindParam.php
	 */
	public function bindParam($name, &$value, $dataType=null, $length=null, $driverOptions=null)
	{
		$this->prepare();
		if($dataType===null)
			$this->_statement->bindParam($name,$value,$this->_connection->getPdoType(gettype($value)));
		else if($length===null)
			$this->_statement->bindParam($name,$value,$dataType);
		else if($driverOptions===null)
			$this->_statement->bindParam($name,$value,$dataType,$length);
		else
			$this->_statement->bindParam($name,$value,$dataType,$length,$driverOptions);
		$this->_paramLog[$name]=&$value;
		return $this;
	}

	/**
	 * Binds a value to a parameter.
	 * @param mixed $name Parameter identifier. For a prepared statement
	 * using named placeholders, this will be a parameter name of
	 * the form :name. For a prepared statement using question mark
	 * placeholders, this will be the 1-indexed position of the parameter.
	 * @param mixed $value The value to bind to the parameter
	 * @param integer $dataType SQL data type of the parameter. If null, the type is determined by the PHP type of the value.
	 * @return CDbCommand the current command being executed
	 * @see http://www.php.net/manual/en/function.PDOStatement-bindValue.php
	 */
	public function bindValue($name, $value, $dataType=null)
	{
		$this->prepare();
		if($dataType===null)
			$this->_statement->bindValue($name,$value,$this->_connection->getPdoType(gettype($value)));
		else
			$this->_statement->bindValue($name,$value,$dataType);
		$this->_paramLog[$name]=$value;
		return $this;
	}

	/**
	 * Binds a list of values to the corresponding parameters.
	 * This is similar to {@link bindValue} except that it binds multiple values.
	 * Note that the SQL data type of each value is determined by its PHP type.
	 * @param array $values the values to be bound. This must be given in terms of an associative
	 * array with array keys being the parameter names, and array values the corresponding parameter values.
	 * For example, <code>array(':name'=>'John', ':age'=>25)</code>.
	 * @return CDbCommand the current command being executed
	 * @since 1.1.5
	 */
	public function bindValues($values)
	{
		$this->prepare();
		foreach($values as $name=>$value)
		{
			$this->_statement->bindValue($name,$value,$this->_connection->getPdoType(gettype($value)));
			$this->_paramLog[$name]=$value;
		}
		return $this;
	}

	/**
	 * Executes the SQL statement.
	 * This method is meant only for executing non-query SQL statement.
	 * No result set will be returned.
	 * @param array $params input parameters (name=>value) for the SQL execution. This is an alternative
	 * to {@link bindParam} and {@link bindValue}. If you have multiple input parameters, passing
	 * them in this way can improve the performance. Note that if you pass parameters in this way,
	 * you cannot bind parameters or values using {@link bindParam} or {@link bindValue}, and vice versa.
	 * binding methods and  the input parameters this way can improve the performance.
	 * @return integer number of rows affected by the execution.
	 * @throws CException execution failed
	 */
	public function execute($params=array())
	{
		if($this->_connection->enableParamLogging && ($pars=array_merge($this->_paramLog,$params))!==array())
		{
			$p=array();
			foreach($pars as $name=>$value)
				$p[$name]=$name.'='.var_export($value,true);
			$par='. Bound with ' .implode(', ',$p);
		}
		else
			$par='';
		Yii::trace('Executing SQL: '.$this->getText().$par,'system.db.CDbCommand');
		try
		{
			if($this->_connection->enableProfiling)
				Yii::beginProfile('system.db.CDbCommand.execute('.$this->getText().$par.')','system.db.CDbCommand.execute');

			$this->prepare();
			if($params===array())
				$this->_statement->execute();
			else
				$this->_statement->execute($params);
			$n=$this->_statement->rowCount();

			if($this->_connection->enableProfiling)
				Yii::endProfile('system.db.CDbCommand.execute('.$this->getText().$par.')','system.db.CDbCommand.execute');

			return $n;
		}
		catch(Exception $e)
		{
			if($this->_connection->enableProfiling)
				Yii::endProfile('system.db.CDbCommand.execute('.$this->getText().$par.')','system.db.CDbCommand.execute');
            $errorInfo = $e instanceof PDOException ? $e->errorInfo : null;
            $message = $e->getMessage();
			Yii::log(Yii::t('yii','CDbCommand::execute() failed: {error}. The SQL statement executed was: {sql}.',
				array('{error}'=>$message, '{sql}'=>$this->getText().$par)),CLogger::LEVEL_ERROR,'system.db.CDbCommand');
            if(YII_DEBUG)
            	$message .= '. The SQL statement executed was: '.$this->getText().$par;
			throw new CDbException(Yii::t('yii','CDbCommand failed to execute the SQL statement: {error}',
				array('{error}'=>$message)),(int)$e->getCode(),$errorInfo);
		}
	}

	/**
	 * Executes the SQL statement and returns query result.
	 * This method is for executing an SQL query that returns result set.
	 * @param array $params input parameters (name=>value) for the SQL execution. This is an alternative
	 * to {@link bindParam} and {@link bindValue}. If you have multiple input parameters, passing
	 * them in this way can improve the performance. Note that if you pass parameters in this way,
	 * you cannot bind parameters or values using {@link bindParam} or {@link bindValue}, and vice versa.
	 * binding methods and  the input parameters this way can improve the performance.
	 * @return CDbDataReader the reader object for fetching the query result
	 * @throws CException execution failed
	 */
	public function query($params=array())
	{
		return $this->queryInternal('',0,$params);
	}

	/**
	 * Executes the SQL statement and returns all rows.
	 * @param boolean $fetchAssociative whether each row should be returned as an associated array with
	 * column names as the keys or the array keys are column indexes (0-based).
	 * @param array $params input parameters (name=>value) for the SQL execution. This is an alternative
	 * to {@link bindParam} and {@link bindValue}. If you have multiple input parameters, passing
	 * them in this way can improve the performance. Note that if you pass parameters in this way,
	 * you cannot bind parameters or values using {@link bindParam} or {@link bindValue}, and vice versa.
	 * binding methods and  the input parameters this way can improve the performance.
	 * @return array all rows of the query result. Each array element is an array representing a row.
	 * An empty array is returned if the query results in nothing.
	 * @throws CException execution failed
	 */
	public function queryAll($fetchAssociative=true,$params=array())
	{
		return $this->queryInternal('fetchAll',$fetchAssociative ? $this->_fetchMode : PDO::FETCH_NUM, $params);
	}

	/**
	 * Executes the SQL statement and returns the first row of the result.
	 * This is a convenient method of {@link query} when only the first row of data is needed.
	 * @param boolean $fetchAssociative whether the row should be returned as an associated array with
	 * column names as the keys or the array keys are column indexes (0-based).
	 * @param array $params input parameters (name=>value) for the SQL execution. This is an alternative
	 * to {@link bindParam} and {@link bindValue}. If you have multiple input parameters, passing
	 * them in this way can improve the performance. Note that if you pass parameters in this way,
	 * you cannot bind parameters or values using {@link bindParam} or {@link bindValue}, and vice versa.
	 * binding methods and  the input parameters this way can improve the performance.
	 * @return mixed the first row (in terms of an array) of the query result, false if no result.
	 * @throws CException execution failed
	 */
	public function queryRow($fetchAssociative=true,$params=array())
	{
		return $this->queryInternal('fetch',$fetchAssociative ? $this->_fetchMode : PDO::FETCH_NUM, $params);
	}

	/**
	 * Executes the SQL statement and returns the value of the first column in the first row of data.
	 * This is a convenient method of {@link query} when only a single scalar
	 * value is needed (e.g. obtaining the count of the records).
	 * @param array $params input parameters (name=>value) for the SQL execution. This is an alternative
	 * to {@link bindParam} and {@link bindValue}. If you have multiple input parameters, passing
	 * them in this way can improve the performance. Note that if you pass parameters in this way,
	 * you cannot bind parameters or values using {@link bindParam} or {@link bindValue}, and vice versa.
	 * binding methods and  the input parameters this way can improve the performance.
	 * @return mixed the value of the first column in the first row of the query result. False is returned if there is no value.
	 * @throws CException execution failed
	 */
	public function queryScalar($params=array())
	{
		$result=$this->queryInternal('fetchColumn',0,$params);
		if(is_resource($result) && get_resource_type($result)==='stream')
			return stream_get_contents($result);
		else
			return $result;
	}

	/**
	 * Executes the SQL statement and returns the first column of the result.
	 * This is a convenient method of {@link query} when only the first column of data is needed.
	 * Note, the column returned will contain the first element in each row of result.
	 * @param array $params input parameters (name=>value) for the SQL execution. This is an alternative
	 * to {@link bindParam} and {@link bindValue}. If you have multiple input parameters, passing
	 * them in this way can improve the performance. Note that if you pass parameters in this way,
	 * you cannot bind parameters or values using {@link bindParam} or {@link bindValue}, and vice versa.
	 * binding methods and  the input parameters this way can improve the performance.
	 * @return array the first column of the query result. Empty array if no result.
	 * @throws CException execution failed
	 */
	public function queryColumn($params=array())
	{
		return $this->queryInternal('fetchAll',PDO::FETCH_COLUMN,$params);
	}

	/**
	 * @param string $method method of PDOStatement to be called
	 * @param mixed $mode parameters to be passed to the method
	 * @param array $params input parameters (name=>value) for the SQL execution. This is an alternative
	 * to {@link bindParam} and {@link bindValue}. If you have multiple input parameters, passing
	 * them in this way can improve the performance. Note that you pass parameters in this way,
	 * you cannot bind parameters or values using {@link bindParam} or {@link bindValue}, and vice versa.
	 * binding methods and  the input parameters this way can improve the performance.
	 * @return mixed the method execution result
	 */
	private function queryInternal($method,$mode,$params=array())
	{
		$params=array_merge($this->params,$params);

		if($this->_connection->enableParamLogging && ($pars=array_merge($this->_paramLog,$params))!==array())
		{
			$p=array();
			foreach($pars as $name=>$value)
				$p[$name]=$name.'='.var_export($value,true);
			$par='. Bound with '.implode(', ',$p);
		}
		else
			$par='';

		Yii::trace('Querying SQL: '.$this->getText().$par,'system.db.CDbCommand');

		if($this->_connection->queryCachingCount>0 && $method!==''
				&& $this->_connection->queryCachingDuration>0
				&& $this->_connection->queryCacheID!==false
				&& ($cache=Yii::app()->getComponent($this->_connection->queryCacheID))!==null)
		{
			$this->_connection->queryCachingCount--;
			$cacheKey='yii:dbquery'.$this->_connection->connectionString.':'.$this->_connection->username;
			$cacheKey.=':'.$this->getText().':'.serialize(array_merge($this->_paramLog,$params));
			if(($result=$cache->get($cacheKey))!==false)
			{
				Yii::trace('Query result found in cache','system.db.CDbCommand');
				return $result;
			}
		}

		try
		{
			if($this->_connection->enableProfiling)
				Yii::beginProfile('system.db.CDbCommand.query('.$this->getText().$par.')','system.db.CDbCommand.query');

			$this->prepare();
			if($params===array())
				$this->_statement->execute();
			else
				$this->_statement->execute($params);

			if($method==='')
				$result=new CDbDataReader($this);
			else
			{
				$mode=(array)$mode;
				$result=call_user_func_array(array($this->_statement, $method), $mode);
				$this->_statement->closeCursor();
			}

			if($this->_connection->enableProfiling)
				Yii::endProfile('system.db.CDbCommand.query('.$this->getText().$par.')','system.db.CDbCommand.query');

			if(isset($cache,$cacheKey))
				$cache->set($cacheKey, $result, $this->_connection->queryCachingDuration, $this->_connection->queryCachingDependency);

			return $result;
		}
		catch(Exception $e)
		{
			if($this->_connection->enableProfiling)
				Yii::endProfile('system.db.CDbCommand.query('.$this->getText().$par.')','system.db.CDbCommand.query');
            $errorInfo = $e instanceof PDOException ? $e->errorInfo : null;
            $message = $e->getMessage();
			Yii::log(Yii::t('yii','CDbCommand::{method}() failed: {error}. The SQL statement executed was: {sql}.',
				array('{method}'=>$method, '{error}'=>$message, '{sql}'=>$this->getText().$par)),CLogger::LEVEL_ERROR,'system.db.CDbCommand');
            if(YII_DEBUG)
            	$message .= '. The SQL statement executed was: '.$this->getText().$par;
			throw new CDbException(Yii::t('yii','CDbCommand failed to execute the SQL statement: {error}',
				array('{error}'=>$message)),(int)$e->getCode(),$errorInfo);
		}
	}

	/**
	 * Builds a SQL SELECT statement from the given query specification.
	 * @param array $query the query specification in name-value pairs. The following
	 * query options are supported: {@link select}, {@link distinct}, {@link from},
	 * {@link where}, {@link join}, {@link group}, {@link having}, {@link order},
	 * {@link limit}, {@link offset} and {@link union}.
	 * @return string the SQL statement
	 * @since 1.1.6
	 */
	public function buildQuery($query)
	{
		$sql=!empty($query['distinct']) ? 'SELECT DISTINCT' : 'SELECT';
		$sql.=' '.(!empty($query['select']) ? $query['select'] : '*');

		if(!empty($query['from']))
			$sql.="\nFROM ".$query['from'];
		else
			throw new CDbException(Yii::t('yii','The DB query must contain the "from" portion.'));

		if(!empty($query['join']))
			$sql.="\n".(is_array($query['join']) ? implode("\n",$query['join']) : $query['join']);

		if(!empty($query['where']))
			$sql.="\nWHERE ".$query['where'];

		if(!empty($query['group']))
			$sql.="\nGROUP BY ".$query['group'];

		if(!empty($query['having']))
			$sql.="\nHAVING ".$query['having'];

		if(!empty($query['order']))
			$sql.="\nORDER BY ".$query['order'];

		$limit=isset($query['limit']) ? (int)$query['limit'] : -1;
		$offset=isset($query['offset']) ? (int)$query['offset'] : -1;
		if($limit>=0 || $offset>0)
			$sql=$this->_connection->getCommandBuilder()->applyLimit($sql,$limit,$offset);

		if(!empty($query['union']))
			$sql.="\nUNION (\n".(is_array($query['union']) ? implode("\n) UNION (\n",$query['union']) : $query['union']) . ')';

		return $sql;
	}

	/**
	 * Sets the SELECT part of the query.
	 * @param mixed $columns the columns to be selected. Defaults to '*', meaning all columns.
	 * Columns can be specified in either a string (e.g. "id, name") or an array (e.g. array('id', 'name')).
	 * Columns can contain table prefixes (e.g. "tbl_user.id") and/or column aliases (e.g. "tbl_user.id AS user_id").
	 * The method will automatically quote the column names unless a column contains some parenthesis
	 * (which means the column contains a DB expression).
	 * @param string $option additional option that should be appended to the 'SELECT' keyword. For example,
	 * in MySQL, the option 'SQL_CALC_FOUND_ROWS' can be used. This parameter is supported since version 1.1.8.
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function select($columns='*', $option='')
	{
		if(is_string($columns) && strpos($columns,'(')!==false)
			$this->_query['select']=$columns;
		else
		{
			if(!is_array($columns))
				$columns=preg_split('/\s*,\s*/',trim($columns),-1,PREG_SPLIT_NO_EMPTY);

			foreach($columns as $i=>$column)
			{
				if(is_object($column))
					$columns[$i]=(string)$column;
				else if(strpos($column,'(')===false)
				{
					if(preg_match('/^(.*?)(?i:\s+as\s+|\s+)(.*)$/',$column,$matches))
						$columns[$i]=$this->_connection->quoteColumnName($matches[1]).' AS '.$this->_connection->quoteColumnName($matches[2]);
					else
						$columns[$i]=$this->_connection->quoteColumnName($column);
				}
			}
			$this->_query['select']=implode(', ',$columns);
		}
		if($option!='')
			$this->_query['select']=$option.' '.$this->_query['select'];
		return $this;
	}

	/**
	 * Returns the SELECT part in the query.
	 * @return string the SELECT part (without 'SELECT') in the query.
	 * @since 1.1.6
	 */
	public function getSelect()
	{
		return isset($this->_query['select']) ? $this->_query['select'] : '';
	}

	/**
	 * Sets the SELECT part in the query.
	 * @param mixed $value the data to be selected. Please refer to {@link select()} for details
	 * on how to specify this parameter.
	 * @since 1.1.6
	 */
	public function setSelect($value)
	{
		$this->select($value);
	}

	/**
	 * Sets the SELECT part of the query with the DISTINCT flag turned on.
	 * This is the same as {@link select} except that the DISTINCT flag is turned on.
	 * @param mixed $columns the columns to be selected. See {@link select} for more details.
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function selectDistinct($columns='*')
	{
		$this->_query['distinct']=true;
		return $this->select($columns);
	}

	/**
	 * Returns a value indicating whether SELECT DISTINCT should be used.
	 * @return boolean a value indicating whether SELECT DISTINCT should be used.
	 * @since 1.1.6
	 */
	public function getDistinct()
	{
		return isset($this->_query['distinct']) ? $this->_query['distinct'] : false;
	}

	/**
	 * Sets a value indicating whether SELECT DISTINCT should be used.
	 * @param boolean $value a value indicating whether SELECT DISTINCT should be used.
	 * @since 1.1.6
	 */
	public function setDistinct($value)
	{
		$this->_query['distinct']=$value;
	}

	/**
	 * Sets the FROM part of the query.
	 * @param mixed $tables the table(s) to be selected from. This can be either a string (e.g. 'tbl_user')
	 * or an array (e.g. array('tbl_user', 'tbl_profile')) specifying one or several table names.
	 * Table names can contain schema prefixes (e.g. 'public.tbl_user') and/or table aliases (e.g. 'tbl_user u').
	 * The method will automatically quote the table names unless it contains some parenthesis
	 * (which means the table is given as a sub-query or DB expression).
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function from($tables)
	{
		if(is_string($tables) && strpos($tables,'(')!==false)
			$this->_query['from']=$tables;
		else
		{
			if(!is_array($tables))
				$tables=preg_split('/\s*,\s*/',trim($tables),-1,PREG_SPLIT_NO_EMPTY);
			foreach($tables as $i=>$table)
			{
				if(strpos($table,'(')===false)
				{
					if(preg_match('/^(.*?)(?i:\s+as\s+|\s+)(.*)$/',$table,$matches))  // with alias
						$tables[$i]=$this->_connection->quoteTableName($matches[1]).' '.$this->_connection->quoteTableName($matches[2]);
					else
						$tables[$i]=$this->_connection->quoteTableName($table);
				}
			}
			$this->_query['from']=implode(', ',$tables);
		}
		return $this;
	}

	/**
	 * Returns the FROM part in the query.
	 * @return string the FROM part (without 'FROM' ) in the query.
	 * @since 1.1.6
	 */
	public function getFrom()
	{
		return isset($this->_query['from']) ? $this->_query['from'] : '';
	}

	/**
	 * Sets the FROM part in the query.
	 * @param mixed $value the tables to be selected from. Please refer to {@link from()} for details
	 * on how to specify this parameter.
	 * @since 1.1.6
	 */
	public function setFrom($value)
	{
		$this->from($value);
	}

	/**
	 * Sets the WHERE part of the query.
	 *
	 * The method requires a $conditions parameter, and optionally a $params parameter
	 * specifying the values to be bound to the query.
	 *
	 * The $conditions parameter should be either a string (e.g. 'id=1') or an array.
	 * If the latter, it must be of the format <code>array(operator, operand1, operand2, ...)</code>,
	 * where the operator can be one of the followings, and the possible operands depend on the corresponding
	 * operator:
	 * <ul>
	 * <li><code>and</code>: the operands should be concatenated together using AND. For example,
	 * array('and', 'id=1', 'id=2') will generate 'id=1 AND id=2'. If an operand is an array,
	 * it will be converted into a string using the same rules described here. For example,
	 * array('and', 'type=1', array('or', 'id=1', 'id=2')) will generate 'type=1 AND (id=1 OR id=2)'.
	 * The method will NOT do any quoting or escaping.</li>
	 * <li><code>or</code>: similar as the <code>and</code> operator except that the operands are concatenated using OR.</li>
	 * <li><code>in</code>: operand 1 should be a column or DB expression, and operand 2 be an array representing
	 * the range of the values that the column or DB expression should be in. For example,
	 * array('in', 'id', array(1,2,3)) will generate 'id IN (1,2,3)'.
	 * The method will properly quote the column name and escape values in the range.</li>
	 * <li><code>not in</code>: similar as the <code>in</code> operator except that IN is replaced with NOT IN in the generated condition.</li>
	 * <li><code>like</code>: operand 1 should be a column or DB expression, and operand 2 be a string or an array representing
	 * the values that the column or DB expression should be like.
	 * For example, array('like', 'name', '%tester%') will generate "name LIKE '%tester%'".
	 * When the value range is given as an array, multiple LIKE predicates will be generated and concatenated using AND.
	 * For example, array('like', 'name', array('%test%', '%sample%')) will generate
	 * "name LIKE '%test%' AND name LIKE '%sample%'".
	 * The method will properly quote the column name and escape values in the range.</li>
	 * <li><code>not like</code>: similar as the <code>like</code> operator except that LIKE is replaced with NOT LIKE in the generated condition.</li>
	 * <li><code>or like</code>: similar as the <code>like</code> operator except that OR is used to concatenated the LIKE predicates.</li>
	 * <li><code>or not like</code>: similar as the <code>not like</code> operator except that OR is used to concatenated the NOT LIKE predicates.</li>
	 * </ul>
	 * @param mixed $conditions the conditions that should be put in the WHERE part.
	 * @param array $params the parameters (name=>value) to be bound to the query
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function where($conditions, $params=array())
	{
		$this->_query['where']=$this->processConditions($conditions);
		foreach($params as $name=>$value)
			$this->params[$name]=$value;
		return $this;
	}

	/**
	 * Returns the WHERE part in the query.
	 * @return string the WHERE part (without 'WHERE' ) in the query.
	 * @since 1.1.6
	 */
	public function getWhere()
	{
		return isset($this->_query['where']) ? $this->_query['where'] : '';
	}

	/**
	 * Sets the WHERE part in the query.
	 * @param mixed $value the where part. Please refer to {@link where()} for details
	 * on how to specify this parameter.
	 * @since 1.1.6
	 */
	public function setWhere($value)
	{
		$this->where($value);
	}

	/**
	 * Appends an INNER JOIN part to the query.
	 * @param string $table the table to be joined.
	 * Table name can contain schema prefix (e.g. 'public.tbl_user') and/or table alias (e.g. 'tbl_user u').
	 * The method will automatically quote the table name unless it contains some parenthesis
	 * (which means the table is given as a sub-query or DB expression).
	 * @param mixed $conditions the join condition that should appear in the ON part.
	 * Please refer to {@link where} on how to specify conditions.
	 * @param array $params the parameters (name=>value) to be bound to the query
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function join($table, $conditions, $params=array())
	{
		return $this->joinInternal('join', $table, $conditions, $params);
	}

	/**
	 * Returns the join part in the query.
	 * @return mixed the join part in the query. This can be an array representing
	 * multiple join fragments, or a string representing a single jojin fragment.
	 * Each join fragment will contain the proper join operator (e.g. LEFT JOIN).
	 * @since 1.1.6
	 */
	public function getJoin()
	{
		return isset($this->_query['join']) ? $this->_query['join'] : '';
	}

	/**
	 * Sets the join part in the query.
	 * @param mixed $value the join part in the query. This can be either a string or
	 * an array representing multiple join parts in the query. Each part must contain
	 * the proper join operator (e.g. 'LEFT JOIN tbl_profile ON tbl_user.id=tbl_profile.id')
	 * @since 1.1.6
	 */
	public function setJoin($value)
	{
		$this->_query['join']=$value;
	}

	/**
	 * Appends a LEFT OUTER JOIN part to the query.
	 * @param string $table the table to be joined.
	 * Table name can contain schema prefix (e.g. 'public.tbl_user') and/or table alias (e.g. 'tbl_user u').
	 * The method will automatically quote the table name unless it contains some parenthesis
	 * (which means the table is given as a sub-query or DB expression).
	 * @param mixed $conditions the join condition that should appear in the ON part.
	 * Please refer to {@link where} on how to specify conditions.
	 * @param array $params the parameters (name=>value) to be bound to the query
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function leftJoin($table, $conditions, $params=array())
	{
		return $this->joinInternal('left join', $table, $conditions, $params);
	}

	/**
	 * Appends a RIGHT OUTER JOIN part to the query.
	 * @param string $table the table to be joined.
	 * Table name can contain schema prefix (e.g. 'public.tbl_user') and/or table alias (e.g. 'tbl_user u').
	 * The method will automatically quote the table name unless it contains some parenthesis
	 * (which means the table is given as a sub-query or DB expression).
	 * @param mixed $conditions the join condition that should appear in the ON part.
	 * Please refer to {@link where} on how to specify conditions.
	 * @param array $params the parameters (name=>value) to be bound to the query
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function rightJoin($table, $conditions, $params=array())
	{
		return $this->joinInternal('right join', $table, $conditions, $params);
	}

	/**
	 * Appends a CROSS JOIN part to the query.
	 * Note that not all DBMS support CROSS JOIN.
	 * @param string $table the table to be joined.
	 * Table name can contain schema prefix (e.g. 'public.tbl_user') and/or table alias (e.g. 'tbl_user u').
	 * The method will automatically quote the table name unless it contains some parenthesis
	 * (which means the table is given as a sub-query or DB expression).
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function crossJoin($table)
	{
		return $this->joinInternal('cross join', $table);
	}

	/**
	 * Appends a NATURAL JOIN part to the query.
	 * Note that not all DBMS support NATURAL JOIN.
	 * @param string $table the table to be joined.
	 * Table name can contain schema prefix (e.g. 'public.tbl_user') and/or table alias (e.g. 'tbl_user u').
	 * The method will automatically quote the table name unless it contains some parenthesis
	 * (which means the table is given as a sub-query or DB expression).
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function naturalJoin($table)
	{
		return $this->joinInternal('natural join', $table);
	}

	/**
	 * Sets the GROUP BY part of the query.
	 * @param mixed $columns the columns to be grouped by.
	 * Columns can be specified in either a string (e.g. "id, name") or an array (e.g. array('id', 'name')).
	 * The method will automatically quote the column names unless a column contains some parenthesis
	 * (which means the column contains a DB expression).
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function group($columns)
	{
		if(is_string($columns) && strpos($columns,'(')!==false)
			$this->_query['group']=$columns;
		else
		{
			if(!is_array($columns))
				$columns=preg_split('/\s*,\s*/',trim($columns),-1,PREG_SPLIT_NO_EMPTY);
			foreach($columns as $i=>$column)
			{
				if(is_object($column))
					$columns[$i]=(string)$column;
				else if(strpos($column,'(')===false)
					$columns[$i]=$this->_connection->quoteColumnName($column);
			}
			$this->_query['group']=implode(', ',$columns);
		}
		return $this;
	}

	/**
	 * Returns the GROUP BY part in the query.
	 * @return string the GROUP BY part (without 'GROUP BY' ) in the query.
	 * @since 1.1.6
	 */
	public function getGroup()
	{
		return isset($this->_query['group']) ? $this->_query['group'] : '';
	}

	/**
	 * Sets the GROUP BY part in the query.
	 * @param mixed $value the GROUP BY part. Please refer to {@link group()} for details
	 * on how to specify this parameter.
	 * @since 1.1.6
	 */
	public function setGroup($value)
	{
		$this->group($value);
	}

	/**
	 * Sets the HAVING part of the query.
	 * @param mixed $conditions the conditions to be put after HAVING.
	 * Please refer to {@link where} on how to specify conditions.
	 * @param array $params the parameters (name=>value) to be bound to the query
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function having($conditions, $params=array())
	{
		$this->_query['having']=$this->processConditions($conditions);
		foreach($params as $name=>$value)
			$this->params[$name]=$value;
		return $this;
	}

	/**
	 * Returns the HAVING part in the query.
	 * @return string the HAVING part (without 'HAVING' ) in the query.
	 * @since 1.1.6
	 */
	public function getHaving()
	{
		return isset($this->_query['having']) ? $this->_query['having'] : '';
	}

	/**
	 * Sets the HAVING part in the query.
	 * @param mixed $value the HAVING part. Please refer to {@link having()} for details
	 * on how to specify this parameter.
	 * @since 1.1.6
	 */
	public function setHaving($value)
	{
		$this->having($value);
	}

	/**
	 * Sets the ORDER BY part of the query.
	 * @param mixed $columns the columns (and the directions) to be ordered by.
	 * Columns can be specified in either a string (e.g. "id ASC, name DESC") or an array (e.g. array('id ASC', 'name DESC')).
	 * The method will automatically quote the column names unless a column contains some parenthesis
	 * (which means the column contains a DB expression).
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function order($columns)
	{
		if(is_string($columns) && strpos($columns,'(')!==false)
			$this->_query['order']=$columns;
		else
		{
			if(!is_array($columns))
				$columns=preg_split('/\s*,\s*/',trim($columns),-1,PREG_SPLIT_NO_EMPTY);
			foreach($columns as $i=>$column)
			{
				if(is_object($column))
					$columns[$i]=(string)$column;
				else if(strpos($column,'(')===false)
				{
					if(preg_match('/^(.*?)\s+(asc|desc)$/i',$column,$matches))
						$columns[$i]=$this->_connection->quoteColumnName($matches[1]).' '.strtoupper($matches[2]);
					else
						$columns[$i]=$this->_connection->quoteColumnName($column);
				}
			}
			$this->_query['order']=implode(', ',$columns);
		}
		return $this;
	}

	/**
	 * Returns the ORDER BY part in the query.
	 * @return string the ORDER BY part (without 'ORDER BY' ) in the query.
	 * @since 1.1.6
	 */
	public function getOrder()
	{
		return isset($this->_query['order']) ? $this->_query['order'] : '';
	}

	/**
	 * Sets the ORDER BY part in the query.
	 * @param mixed $value the ORDER BY part. Please refer to {@link order()} for details
	 * on how to specify this parameter.
	 * @since 1.1.6
	 */
	public function setOrder($value)
	{
		$this->order($value);
	}

	/**
	 * Sets the LIMIT part of the query.
	 * @param integer $limit the limit
	 * @param integer $offset the offset
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function limit($limit, $offset=null)
	{
		$this->_query['limit']=(int)$limit;
		if($offset!==null)
			$this->offset($offset);
		return $this;
	}

	/**
	 * Returns the LIMIT part in the query.
	 * @return string the LIMIT part (without 'LIMIT' ) in the query.
	 * @since 1.1.6
	 */
	public function getLimit()
	{
		return isset($this->_query['limit']) ? $this->_query['limit'] : -1;
	}

	/**
	 * Sets the LIMIT part in the query.
	 * @param integer $value the LIMIT part. Please refer to {@link limit()} for details
	 * on how to specify this parameter.
	 * @since 1.1.6
	 */
	public function setLimit($value)
	{
		$this->limit($value);
	}

	/**
	 * Sets the OFFSET part of the query.
	 * @param integer $offset the offset
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function offset($offset)
	{
		$this->_query['offset']=(int)$offset;
		return $this;
	}

	/**
	 * Returns the OFFSET part in the query.
	 * @return string the OFFSET part (without 'OFFSET' ) in the query.
	 * @since 1.1.6
	 */
	public function getOffset()
	{
		return isset($this->_query['offset']) ? $this->_query['offset'] : -1;
	}

	/**
	 * Sets the OFFSET part in the query.
	 * @param integer $value the OFFSET part. Please refer to {@link offset()} for details
	 * on how to specify this parameter.
	 * @since 1.1.6
	 */
	public function setOffset($value)
	{
		$this->offset($value);
	}

	/**
	 * Appends a SQL statement using UNION operator.
	 * @param string $sql the SQL statement to be appended using UNION
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	public function union($sql)
	{
		if(isset($this->_query['union']) && is_string($this->_query['union']))
			$this->_query['union']=array($this->_query['union']);

		$this->_query['union'][]=$sql;

		return $this;
	}

	/**
	 * Returns the UNION part in the query.
	 * @return mixed the UNION part (without 'UNION' ) in the query.
	 * This can be either a string or an array representing multiple union parts.
	 * @since 1.1.6
	 */
	public function getUnion()
	{
		return isset($this->_query['union']) ? $this->_query['union'] : '';
	}

	/**
	 * Sets the UNION part in the query.
	 * @param mixed $value the UNION part. This can be either a string or an array
	 * representing multiple SQL statements to be unioned together.
	 * @since 1.1.6
	 */
	public function setUnion($value)
	{
		$this->_query['union']=$value;
	}

	/**
	 * Creates and executes an INSERT SQL statement.
	 * The method will properly escape the column names, and bind the values to be inserted.
	 * @param string $table the table that new rows will be inserted into.
	 * @param array $columns the column data (name=>value) to be inserted into the table.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function insert($table, $columns)
	{
		$params=array();
		$names=array();
		$placeholders=array();
		foreach($columns as $name=>$value)
		{
			$names[]=$this->_connection->quoteColumnName($name);
			if($value instanceof CDbExpression)
			{
				$placeholders[] = $value->expression;
				foreach($value->params as $n => $v)
					$params[$n] = $v;
			}
			else
			{
				$placeholders[] = ':' . $name;
				$params[':' . $name] = $value;
			}
		}
		$sql='INSERT INTO ' . $this->_connection->quoteTableName($table)
			. ' (' . implode(', ',$names) . ') VALUES ('
			. implode(', ', $placeholders) . ')';
		return $this->setText($sql)->execute($params);
	}

	/**
	 * Creates and executes an UPDATE SQL statement.
	 * The method will properly escape the column names and bind the values to be updated.
	 * @param string $table the table to be updated.
	 * @param array $columns the column data (name=>value) to be updated.
	 * @param mixed $conditions the conditions that will be put in the WHERE part. Please
	 * refer to {@link where} on how to specify conditions.
	 * @param array $params the parameters to be bound to the query.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function update($table, $columns, $conditions='', $params=array())
	{
		$lines=array();
		foreach($columns as $name=>$value)
		{
			if($value instanceof CDbExpression)
			{
				$lines[]=$this->_connection->quoteColumnName($name) . '=' . $value->expression;
				foreach($value->params as $n => $v)
					$params[$n] = $v;
			}
			else
			{
				$lines[]=$this->_connection->quoteColumnName($name) . '=:' . $name;
				$params[':' . $name]=$value;
			}
		}
		$sql='UPDATE ' . $this->_connection->quoteTableName($table) . ' SET ' . implode(', ', $lines);
		if(($where=$this->processConditions($conditions))!='')
			$sql.=' WHERE '.$where;
		return $this->setText($sql)->execute($params);
	}

	/**
	 * Creates and executes a DELETE SQL statement.
	 * @param string $table the table where the data will be deleted from.
	 * @param mixed $conditions the conditions that will be put in the WHERE part. Please
	 * refer to {@link where} on how to specify conditions.
	 * @param array $params the parameters to be bound to the query.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function delete($table, $conditions='', $params=array())
	{
		$sql='DELETE FROM ' . $this->_connection->quoteTableName($table);
		if(($where=$this->processConditions($conditions))!='')
			$sql.=' WHERE '.$where;
		return $this->setText($sql)->execute($params);
	}

	/**
	 * Builds and executes a SQL statement for creating a new DB table.
	 *
	 * The columns in the new  table should be specified as name-definition pairs (e.g. 'name'=>'string'),
	 * where name stands for a column name which will be properly quoted by the method, and definition
	 * stands for the column type which can contain an abstract DB type.
	 * The {@link getColumnType} method will be invoked to convert any abstract type into a physical one.
	 *
	 * If a column is specified with definition only (e.g. 'PRIMARY KEY (name, type)'), it will be directly
	 * inserted into the generated SQL.
	 *
	 * @param string $table the name of the table to be created. The name will be properly quoted by the method.
	 * @param array $columns the columns (name=>definition) in the new table.
	 * @param string $options additional SQL fragment that will be appended to the generated SQL.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function createTable($table, $columns, $options=null)
	{
		return $this->setText($this->getConnection()->getSchema()->createTable($table, $columns, $options))->execute();
	}

	/**
	 * Builds and executes a SQL statement for renaming a DB table.
	 * @param string $table the table to be renamed. The name will be properly quoted by the method.
	 * @param string $newName the new table name. The name will be properly quoted by the method.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function renameTable($table, $newName)
	{
		return $this->setText($this->getConnection()->getSchema()->renameTable($table, $newName))->execute();
	}

	/**
	 * Builds and executes a SQL statement for dropping a DB table.
	 * @param string $table the table to be dropped. The name will be properly quoted by the method.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function dropTable($table)
	{
		return $this->setText($this->getConnection()->getSchema()->dropTable($table))->execute();
	}

	/**
	 * Builds and executes a SQL statement for truncating a DB table.
	 * @param string $table the table to be truncated. The name will be properly quoted by the method.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function truncateTable($table)
	{
		$schema=$this->getConnection()->getSchema();
		$n=$this->setText($schema->truncateTable($table))->execute();
		if(strncasecmp($this->getConnection()->getDriverName(),'sqlite',6)===0)
			$schema->resetSequence($schema->getTable($table));
		return $n;
	}

	/**
	 * Builds and executes a SQL statement for adding a new DB column.
	 * @param string $table the table that the new column will be added to. The table name will be properly quoted by the method.
	 * @param string $column the name of the new column. The name will be properly quoted by the method.
	 * @param string $type the column type. The {@link getColumnType} method will be invoked to convert abstract column type (if any)
	 * into the physical one. Anything that is not recognized as abstract type will be kept in the generated SQL.
	 * For example, 'string' will be turned into 'varchar(255)', while 'string not null' will become 'varchar(255) not null'.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function addColumn($table, $column, $type)
	{
		return $this->setText($this->getConnection()->getSchema()->addColumn($table, $column, $type))->execute();
	}

	/**
	 * Builds and executes a SQL statement for dropping a DB column.
	 * @param string $table the table whose column is to be dropped. The name will be properly quoted by the method.
	 * @param string $column the name of the column to be dropped. The name will be properly quoted by the method.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function dropColumn($table, $column)
	{
		return $this->setText($this->getConnection()->getSchema()->dropColumn($table, $column))->execute();
	}

	/**
	 * Builds and executes a SQL statement for renaming a column.
	 * @param string $table the table whose column is to be renamed. The name will be properly quoted by the method.
	 * @param string $name the old name of the column. The name will be properly quoted by the method.
	 * @param string $newName the new name of the column. The name will be properly quoted by the method.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function renameColumn($table, $name, $newName)
	{
		return $this->setText($this->getConnection()->getSchema()->renameColumn($table, $name, $newName))->execute();
	}

	/**
	 * Builds and executes a SQL statement for changing the definition of a column.
	 * @param string $table the table whose column is to be changed. The table name will be properly quoted by the method.
	 * @param string $column the name of the column to be changed. The name will be properly quoted by the method.
	 * @param string $type the new column type. The {@link getColumnType} method will be invoked to convert abstract column type (if any)
	 * into the physical one. Anything that is not recognized as abstract type will be kept in the generated SQL.
	 * For example, 'string' will be turned into 'varchar(255)', while 'string not null' will become 'varchar(255) not null'.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function alterColumn($table, $column, $type)
	{
		return $this->setText($this->getConnection()->getSchema()->alterColumn($table, $column, $type))->execute();
	}

	/**
	 * Builds a SQL statement for adding a foreign key constraint to an existing table.
	 * The method will properly quote the table and column names.
	 * @param string $name the name of the foreign key constraint.
	 * @param string $table the table that the foreign key constraint will be added to.
	 * @param string $columns the name of the column to that the constraint will be added on. If there are multiple columns, separate them with commas.
	 * @param string $refTable the table that the foreign key references to.
	 * @param string $refColumns the name of the column that the foreign key references to. If there are multiple columns, separate them with commas.
	 * @param string $delete the ON DELETE option. Most DBMS support these options: RESTRICT, CASCADE, NO ACTION, SET DEFAULT, SET NULL
	 * @param string $update the ON UPDATE option. Most DBMS support these options: RESTRICT, CASCADE, NO ACTION, SET DEFAULT, SET NULL
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function addForeignKey($name, $table, $columns, $refTable, $refColumns, $delete=null, $update=null)
	{
		return $this->setText($this->getConnection()->getSchema()->addForeignKey($name, $table, $columns, $refTable, $refColumns, $delete, $update))->execute();
	}

	/**
	 * Builds a SQL statement for dropping a foreign key constraint.
	 * @param string $name the name of the foreign key constraint to be dropped. The name will be properly quoted by the method.
	 * @param string $table the table whose foreign is to be dropped. The name will be properly quoted by the method.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function dropForeignKey($name, $table)
	{
		return $this->setText($this->getConnection()->getSchema()->dropForeignKey($name, $table))->execute();
	}

	/**
	 * Builds and executes a SQL statement for creating a new index.
	 * @param string $name the name of the index. The name will be properly quoted by the method.
	 * @param string $table the table that the new index will be created for. The table name will be properly quoted by the method.
	 * @param string $column the column(s) that should be included in the index. If there are multiple columns, please separate them
	 * by commas. The column names will be properly quoted by the method.
	 * @param boolean $unique whether to add UNIQUE constraint on the created index.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function createIndex($name, $table, $column, $unique=false)
	{
		return $this->setText($this->getConnection()->getSchema()->createIndex($name, $table, $column, $unique))->execute();
	}

	/**
	 * Builds and executes a SQL statement for dropping an index.
	 * @param string $name the name of the index to be dropped. The name will be properly quoted by the method.
	 * @param string $table the table whose index is to be dropped. The name will be properly quoted by the method.
	 * @return integer number of rows affected by the execution.
	 * @since 1.1.6
	 */
	public function dropIndex($name, $table)
	{
		return $this->setText($this->getConnection()->getSchema()->dropIndex($name, $table))->execute();
	}

	/**
	 * Generates the condition string that will be put in the WHERE part
	 * @param mixed $conditions the conditions that will be put in the WHERE part.
	 * @return string the condition string to put in the WHERE part
	 */
	private function processConditions($conditions)
	{
		if(!is_array($conditions))
			return $conditions;
		else if($conditions===array())
			return '';
		$n=count($conditions);
		$operator=strtoupper($conditions[0]);
		if($operator==='OR' || $operator==='AND')
		{
			$parts=array();
			for($i=1;$i<$n;++$i)
			{
				$condition=$this->processConditions($conditions[$i]);
				if($condition!=='')
					$parts[]='('.$condition.')';
			}
			return $parts===array() ? '' : implode(' '.$operator.' ', $parts);
		}

		if(!isset($conditions[1],$conditions[2]))
			return '';

		$column=$conditions[1];
		if(strpos($column,'(')===false)
			$column=$this->_connection->quoteColumnName($column);

		$values=$conditions[2];
		if(!is_array($values))
			$values=array($values);

		if($operator==='IN' || $operator==='NOT IN')
		{
			if($values===array())
				return $operator==='IN' ? '0=1' : '';
			foreach($values as $i=>$value)
			{
				if(is_string($value))
					$values[$i]=$this->_connection->quoteValue($value);
				else
					$values[$i]=(string)$value;
			}
			return $column.' '.$operator.' ('.implode(', ',$values).')';
		}

		if($operator==='LIKE' || $operator==='NOT LIKE' || $operator==='OR LIKE' || $operator==='OR NOT LIKE')
		{
			if($values===array())
				return $operator==='LIKE' || $operator==='OR LIKE' ? '0=1' : '';

			if($operator==='LIKE' || $operator==='NOT LIKE')
				$andor=' AND ';
			else
			{
				$andor=' OR ';
				$operator=$operator==='OR LIKE' ? 'LIKE' : 'NOT LIKE';
			}
			$expressions=array();
			foreach($values as $value)
				$expressions[]=$column.' '.$operator.' '.$this->_connection->quoteValue($value);
			return implode($andor,$expressions);
		}

		throw new CDbException(Yii::t('yii', 'Unknown operator "{operator}".', array('{operator}'=>$operator)));
	}

	/**
	 * Appends an JOIN part to the query.
	 * @param string $type the join type ('join', 'left join', 'right join', 'cross join', 'natural join')
	 * @param string $table the table to be joined.
	 * Table name can contain schema prefix (e.g. 'public.tbl_user') and/or table alias (e.g. 'tbl_user u').
	 * The method will automatically quote the table name unless it contains some parenthesis
	 * (which means the table is given as a sub-query or DB expression).
	 * @param mixed $conditions the join condition that should appear in the ON part.
	 * Please refer to {@link where} on how to specify conditions.
	 * @param array $params the parameters (name=>value) to be bound to the query
	 * @return CDbCommand the command object itself
	 * @since 1.1.6
	 */
	private function joinInternal($type, $table, $conditions='', $params=array())
	{
		if(strpos($table,'(')===false)
		{
			if(preg_match('/^(.*?)(?i:\s+as\s+|\s+)(.*)$/',$table,$matches))  // with alias
				$table=$this->_connection->quoteTableName($matches[1]).' '.$this->_connection->quoteTableName($matches[2]);
			else
				$table=$this->_connection->quoteTableName($table);
		}

		$conditions=$this->processConditions($conditions);
		if($conditions!='')
			$conditions=' ON '.$conditions;

		if(isset($this->_query['join']) && is_string($this->_query['join']))
			$this->_query['join']=array($this->_query['join']);

		$this->_query['join'][]=strtoupper($type) . ' ' . $table . $conditions;

		foreach($params as $name=>$value)
			$this->params[$name]=$value;
		return $this;
	}
}