diff --git a/framework/db/dao/Command.php b/framework/db/dao/Command.php
index ecb10fb..3fa762f 100644
--- a/framework/db/dao/Command.php
+++ b/framework/db/dao/Command.php
@@ -50,12 +50,19 @@ class Command extends \yii\base\Component
 	 */
 	public $params = array();
 
-	private $_connection;
-	private $_text;
-	private $_statement;
+	public $connection;
+	public $query;
+	public $pdoStatement;
+
+	private $_sql;
 	private $_paramLog = array();
-	private $_query;
-	private $_fetchMode = array(PDO::FETCH_ASSOC);
+	/**
+	 * Set the default fetch mode for this statement
+	 * @param mixed $mode fetch mode
+	 * @return Command
+	 * @see http://www.php.net/manual/en/function.PDOStatement-setFetchMode.php
+	 */
+	public $fetchMode = \PDO::FETCH_ASSOC;
 
 	/**
 	 * Constructor.
@@ -80,38 +87,19 @@ class Command extends \yii\base\Component
 	 */
 	public function __construct($connection, $query = null)
 	{
-		$this->_connection = $connection;
-		if (is_array($query))
-		{
-			foreach ($query as $name => $value)
-				$this->$name = $value;
+		$this->connection = $connection;
+		if (is_object($query)) {
+			$this->query = $query;
+		}
+		else {
+			$this->query = new Query;
+			if (is_array($this->query)) {
+				$this->query->fromArray($this->query);
+			}
+			else {
+				$this->_sql = $query;
+			}
 		}
-		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 $mode fetch mode
-	 * @return Command
-	 * @see http://www.php.net/manual/en/function.PDOStatement-setFetchMode.php
-	 * @since 1.1.7
-	 */
-	public function setFetchMode($mode)
-	{
-		$params = func_get_args();
-		$this->_fetchMode = $params;
-		return $this;
 	}
 
 	/**
@@ -124,9 +112,9 @@ class Command extends \yii\base\Component
 	 */
 	public function reset()
 	{
-		$this->_text = null;
-		$this->_query = null;
-		$this->_statement = null;
+		$this->_sql = null;
+		$this->query = new Query;
+		$this->pdoStatement = null;
 		$this->_paramLog = array();
 		$this->params = array();
 		return $this;
@@ -135,11 +123,12 @@ class Command extends \yii\base\Component
 	/**
 	 * @return string the SQL statement to be executed
 	 */
-	public function getText()
+	public function getSql()
 	{
-		if ($this->_text == '' && !empty($this->_query))
-			$this->setText($this->buildQuery($this->_query));
-		return $this->_text;
+		if ($this->_sql == '' && is_object($this->query)) {
+			$this->_sql = $this->query->getSql($this->connection);
+		}
+		return $this->_sql;
 	}
 
 	/**
@@ -148,34 +137,19 @@ class Command extends \yii\base\Component
 	 * @param string $value the SQL statement to be executed
 	 * @return Command this command instance
 	 */
-	public function setText($value)
+	public function setSql($value)
 	{
-		if ($this->_connection->tablePrefix !== null && $value != '')
-			$this->_text = preg_replace('/{{(.*?)}}/', $this->_connection->tablePrefix . '\1', $value);
-		else
-			$this->_text = $value;
+		if ($this->connection->tablePrefix !== null && strpos($value, '{') !== false) {
+			$this->_sql = preg_replace('/{{(.*?)}}/', $this->connection->tablePrefix . '\1', $value);
+		}
+		else {
+			$this->_sql = $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 $this->_statement;
-	}
-
-	/**
 	 * Prepares the SQL statement to be executed.
 	 * For complex SQL statement that is to be executed multiple times,
 	 * this may improve performance.
@@ -184,18 +158,15 @@ class Command extends \yii\base\Component
 	 */
 	public function prepare()
 	{
-		if ($this->_statement == null)
-		{
-			try
-			{
-				$this->_statement = $this->getConnection()->getPdoInstance()->prepare($this->getText());
+		if ($this->pdoStatement == null) {
+			try {
+				$this->pdoStatement = $this->connection->pdo->prepare($this->getSql());
 				$this->_paramLog = array();
 			}
-			catch(Exception $e)
-			{
-				Yii::log('Error in preparing SQL: ' . $this->getText(), CLogger::LEVEL_ERROR, 'system.db.Command');
-                $errorInfo = $e instanceof PDOException ? $e->errorInfo : null;
-				throw new CDbException(Yii::t('yii', 'Command failed to prepare the SQL statement: {error}',
+			catch(Exception $e) {
+				Yii::log('Error in preparing SQL: ' . $this->getSql(), CLogger::LEVEL_ERROR, 'system.db.Command');
+                $errorInfo = $e instanceof \PDOException ? $e->errorInfo : null;
+				throw new Exception('Unable to prepare the SQL statement: {error}',
 					array('{error}' => $e->getMessage())), (int)$e->getCode(), $errorInfo);
 			}
 		}
@@ -206,7 +177,7 @@ class Command extends \yii\base\Component
 	 */
 	public function cancel()
 	{
-		$this->_statement = null;
+		$this->pdoStatement = null;
 	}
 
 	/**
@@ -226,13 +197,13 @@ class Command extends \yii\base\Component
 	{
 		$this->prepare();
 		if ($dataType === null)
-			$this->_statement->bindParam($name, $value, $this->_connection->getPdoType(gettype($value)));
+			$this->pdoStatement->bindParam($name, $value, $this->connection->getPdoType(gettype($value)));
 		elseif ($length === null)
-			$this->_statement->bindParam($name, $value, $dataType);
+			$this->pdoStatement->bindParam($name, $value, $dataType);
 		elseif ($driverOptions === null)
-			$this->_statement->bindParam($name, $value, $dataType, $length);
+			$this->pdoStatement->bindParam($name, $value, $dataType, $length);
 		else
-			$this->_statement->bindParam($name, $value, $dataType, $length, $driverOptions);
+			$this->pdoStatement->bindParam($name, $value, $dataType, $length, $driverOptions);
 		$this->_paramLog[$name] =& $value;
 		return $this;
 	}
@@ -252,9 +223,9 @@ class Command extends \yii\base\Component
 	{
 		$this->prepare();
 		if ($dataType === null)
-			$this->_statement->bindValue($name, $value, $this->_connection->getPdoType(gettype($value)));
+			$this->pdoStatement->bindValue($name, $value, $this->connection->getPdoType(gettype($value)));
 		else
-			$this->_statement->bindValue($name, $value, $dataType);
+			$this->pdoStatement->bindValue($name, $value, $dataType);
 		$this->_paramLog[$name] = $value;
 		return $this;
 	}
@@ -274,7 +245,7 @@ class Command extends \yii\base\Component
 		$this->prepare();
 		foreach ($values as $name => $value)
 		{
-			$this->_statement->bindValue($name, $value, $this->_connection->getPdoType(gettype($value)));
+			$this->pdoStatement->bindValue($name, $value, $this->connection->getPdoType(gettype($value)));
 			$this->_paramLog[$name] = $value;
 		}
 		return $this;
@@ -295,7 +266,7 @@ class Command extends \yii\base\Component
 	 */
 	public function execute($params = array())
 	{
-		if ($this->_connection->enableParamLogging && ($pars = array_merge($this->_paramLog, $params)) !== array())
+		if ($this->connection->enableParamLogging && ($pars = array_merge($this->_paramLog, $params)) !== array())
 		{
 			$p = array();
 			foreach ($pars as $name => $value)
@@ -304,34 +275,34 @@ class Command extends \yii\base\Component
 		}
 		else
 			$par = '';
-		Yii::trace('Executing SQL: ' . $this->getText() . $par, 'system.db.Command');
+		Yii::trace('Executing SQL: ' . $this->getSql() . $par, 'system.db.Command');
 		try
 		{
-			if ($this->_connection->enableProfiling)
-				Yii::beginProfile('system.db.Command.execute(' . $this->getText() . ')', 'system.db.Command.execute');
+			if ($this->connection->enableProfiling)
+				Yii::beginProfile('system.db.Command.execute(' . $this->getSql() . ')', 'system.db.Command.execute');
 
 			$this->prepare();
 			if ($params === array())
-				$this->_statement->execute();
+				$this->pdoStatement->execute();
 			else
-				$this->_statement->execute($params);
-			$n = $this->_statement->rowCount();
+				$this->pdoStatement->execute($params);
+			$n = $this->pdoStatement->rowCount();
 
-			if ($this->_connection->enableProfiling)
-				Yii::endProfile('system.db.Command.execute(' . $this->getText() . ')', 'system.db.Command.execute');
+			if ($this->connection->enableProfiling)
+				Yii::endProfile('system.db.Command.execute(' . $this->getSql() . ')', 'system.db.Command.execute');
 
 			return $n;
 		}
 		catch(Exception $e)
 		{
-			if ($this->_connection->enableProfiling)
-				Yii::endProfile('system.db.Command.execute(' . $this->getText() . ')', 'system.db.Command.execute');
+			if ($this->connection->enableProfiling)
+				Yii::endProfile('system.db.Command.execute(' . $this->getSql() . ')', 'system.db.Command.execute');
             $errorInfo = $e instanceof PDOException ? $e->errorInfo : null;
             $message = $e->getMessage();
 			Yii::log(Yii::t('yii', 'Command::execute() failed: {error}. The SQL statement executed was: {sql}.',
-				array('{error}' => $message, '{sql}' => $this->getText() . $par)), CLogger::LEVEL_ERROR, 'system.db.Command');
+				array('{error}' => $message, '{sql}' => $this->getSql() . $par)), CLogger::LEVEL_ERROR, 'system.db.Command');
             if (YII_DEBUG)
-            	$message .= '. The SQL statement executed was: ' . $this->getText() . $par;
+            	$message .= '. The SQL statement executed was: ' . $this->getSql() . $par;
 			throw new CDbException(Yii::t('yii', 'Command failed to execute the SQL statement: {error}',
 				array('{error}' => $message)), (int)$e->getCode(), $errorInfo);
 		}
@@ -351,7 +322,7 @@ class Command extends \yii\base\Component
 	 */
 	public function query($params = array())
 	{
-		return $this->queryInternal('', 0, $params);
+		return $this->queryInternal('', $params);
 	}
 
 	/**
@@ -368,9 +339,9 @@ class Command extends \yii\base\Component
 	 * An empty array is returned if the query results in nothing.
 	 * @throws CException execution failed
 	 */
-	public function queryAll($fetchAssociative = true, $params = array())
+	public function queryAll($params = array(), $fetchMode = null)
 	{
-		return $this->queryInternal('fetchAll', $fetchAssociative ? $this->_fetchMode : PDO::FETCH_NUM, $params);
+		return $this->queryInternal('fetchAll', $params, $fetchMode);
 	}
 
 	/**
@@ -387,9 +358,9 @@ class Command extends \yii\base\Component
 	 * @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, $params = array())
+	public function queryRow($params = array(), $fetchMode = null)
 	{
-		return $this->queryInternal('fetch', $fetchAssociative ? $this->_fetchMode : PDO::FETCH_NUM, $params);
+		return $this->queryInternal('fetch', $params, $fetchMode);
 	}
 
 	/**
@@ -407,11 +378,13 @@ class Command extends \yii\base\Component
 	 */
 	public function queryScalar($params = array())
 	{
-		$result = $this->queryInternal('fetchColumn', 0, $params);
-		if (is_resource($result) && get_resource_type($result) === 'stream')
+		$result = $this->queryInternal('fetchColumn', $params);
+		if (is_resource($result) && get_resource_type($result) === 'stream') {
 			return stream_get_contents($result);
-		else
+		}
+		else {
 			return $result;
+		}
 	}
 
 	/**
@@ -429,7 +402,7 @@ class Command extends \yii\base\Component
 	 */
 	public function queryColumn($params = array())
 	{
-		return $this->queryInternal('fetchAll', PDO::FETCH_COLUMN, $params);
+		return $this->queryInternal('fetchAll', $params, \PDO::FETCH_COLUMN);
 	}
 
 	/**
@@ -443,11 +416,11 @@ class Command extends \yii\base\Component
 	 * This parameter has been available since version 1.0.10.
 	 * @return mixed the method execution result
 	 */
-	private function queryInternal($method, $mode, $params = array())
+	private function queryInternal($method, $params, $fetchMode = null)
 	{
 		$params = array_merge($this->params, $params);
 
-		if ($this->_connection->enableParamLogging && ($pars = array_merge($this->_paramLog, $params)) !== array())
+		if ($this->connection->enableParamLogging && ($pars = array_merge($this->_paramLog, $params)) !== array())
 		{
 			$p = array();
 			foreach ($pars as $name => $value)
@@ -457,16 +430,16 @@ class Command extends \yii\base\Component
 		else
 			$par = '';
 
-		Yii::trace('Querying SQL: ' . $this->getText() . $par, 'system.db.Command');
+		Yii::trace('Querying SQL: ' . $this->getSql() . $par, 'system.db.Command');
 
-		if ($this->_connection->queryCachingCount > 0 && $method !== ''
-				&& $this->_connection->queryCachingDuration > 0
-				&& $this->_connection->queryCacheID !== false
-				&& ($cache = Yii::app()->getComponent($this->_connection->queryCacheID)) !== null)
+		if ($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));
+			$this->connection->queryCachingCount--;
+			$cacheKey = 'yii:dbquery' . $this->connection->connectionString . ':' . $this->connection->username;
+			$cacheKey .= ':' . $this->getSql() . ':' . serialize(array_merge($this->_paramLog, $params));
 			if (($result = $cache->get($cacheKey)) !== false)
 			{
 				Yii::trace('Query result found in cache', 'system.db.Command');
@@ -476,93 +449,50 @@ class Command extends \yii\base\Component
 
 		try
 		{
-			if ($this->_connection->enableProfiling)
-				Yii::beginProfile('system.db.Command.query(' . $this->getText() . $par . ')', 'system.db.Command.query');
+			if ($this->connection->enableProfiling)
+				Yii::beginProfile('system.db.Command.query(' . $this->getSql() . $par . ')', 'system.db.Command.query');
 
 			$this->prepare();
 			if ($params === array())
-				$this->_statement->execute();
+				$this->pdoStatement->execute();
 			else
-				$this->_statement->execute($params);
+				$this->pdoStatement->execute($params);
 
 			if ($method === '')
-				$result = new CDbDataReader($this);
+				$result = new DataReader($this);
 			else
 			{
-				$mode = (array)$mode;
-				$result = call_user_func_array(array($this->_statement, $method), $mode);
-				$this->_statement->closeCursor();
+		 		if ($fetchMode === null) {
+		 			$fetchMode = $this->fetchMode;
+		 		}
+				$result = call_user_func_array(array($this->pdoStatement, $method), (array)$fetchMode);
+				$this->pdoStatement->closeCursor();
 			}
 
-			if ($this->_connection->enableProfiling)
-				Yii::endProfile('system.db.Command.query(' . $this->getText() . $par . ')', 'system.db.Command.query');
+			if ($this->connection->enableProfiling)
+				Yii::endProfile('system.db.Command.query(' . $this->getSql() . $par . ')', 'system.db.Command.query');
 
 			if (isset($cache, $cacheKey))
-				$cache->set($cacheKey, $result, $this->_connection->queryCachingDuration, $this->_connection->queryCachingDependency);
+				$cache->set($cacheKey, $result, $this->connection->queryCachingDuration, $this->connection->queryCachingDependency);
 
 			return $result;
 		}
 		catch(Exception $e)
 		{
-			if ($this->_connection->enableProfiling)
-				Yii::endProfile('system.db.Command.query(' . $this->getText() . $par . ')', 'system.db.Command.query');
+			if ($this->connection->enableProfiling)
+				Yii::endProfile('system.db.Command.query(' . $this->getSql() . $par . ')', 'system.db.Command.query');
             $errorInfo = $e instanceof PDOException ? $e->errorInfo : null;
             $message = $e->getMessage();
 			Yii::log(Yii::t('yii', 'Command::{method}() failed: {error}. The SQL statement executed was: {sql}.',
-				array('{method}' => $method, '{error}' => $message, '{sql}' => $this->getText() . $par)), CLogger::LEVEL_ERROR, 'system.db.Command');
+				array('{method}' => $method, '{error}' => $message, '{sql}' => $this->getSql() . $par)), CLogger::LEVEL_ERROR, 'system.db.Command');
             if (YII_DEBUG)
-            	$message .= '. The SQL statement executed was: ' . $this->getText() . $par;
+            	$message .= '. The SQL statement executed was: ' . $this->getSql() . $par;
 			throw new CDbException(Yii::t('yii', 'Command 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)
-	{
-		$sql = isset($query['distinct']) && $query['distinct'] ? 'SELECT DISTINCT' : 'SELECT';
-		$sql .= ' ' . (isset($query['select']) ? $query['select'] : '*');
-
-		if (isset($query['from']))
-			$sql .= "\nFROM " . $query['from'];
-		else
-			throw new CDbException(Yii::t('yii', 'The DB query must contain the "from" portion.'));
-
-		if (isset($query['join']))
-			$sql .= "\n" . (is_array($query['join']) ? implode("\n", $query['join']) : $query['join']);
-
-		if (isset($query['where']))
-			$sql .= "\nWHERE " . $query['where'];
-
-		if (isset($query['group']))
-			$sql .= "\nGROUP BY " . $query['group'];
-
-		if (isset($query['having']))
-			$sql .= "\nHAVING " . $query['having'];
-
-		if (isset($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, $offset);
-
-		if (isset($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 $columns the columns to be selected. Defaults to '*', meaning all columns.
 	 * Columns can be specified in either a string (e.g. "id, name") or an array (e.g. array('id', 'name')).
@@ -576,84 +506,22 @@ class Command extends \yii\base\Component
 	 */
 	public function select($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)$column;
-				elseif (strpos($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'];
+		$this->query->select = $columns;
+		$this->query->selectOption = $option;
 		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 $columns the columns to be selected. See {@link select} for more details.
 	 * @return Command the command object itself
 	 * @since 1.1.6
 	 */
-	public function selectDistinct($columns = '*')
+	public function selectDistinct($columns = '*', $option = '')
 	{
-		$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;
+		$this->query->distinct = true;
+		return $this->select($columns, $option);
 	}
 
 	/**
@@ -668,49 +536,11 @@ class Command extends \yii\base\Component
 	 */
 	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);
-		}
+		$this->query->from = $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 $params parameter
@@ -750,34 +580,12 @@ class Command extends \yii\base\Component
 	 */
 	public function where($conditions, $params = array())
 	{
-		$this->_query['where'] = $this->processConditions($conditions);
-		foreach ($params as $name => $value)
-			$this->params[$name] = $value;
+		$this->query->where = $conditions;
+		$this->query->addParams($params);
 		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 $table the table to be joined.
 	 * Table name can contain schema prefix (e.g. 'public.tbl_user') and/or table alias (e.g. 'tbl_user u').
@@ -791,31 +599,7 @@ class Command extends \yii\base\Component
 	 */
 	public function join($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;
+		return $this->joinInternal('JOIN', $table, $conditions, $params);
 	}
 
 	/**
@@ -832,7 +616,7 @@ class Command extends \yii\base\Component
 	 */
 	public function leftJoin($table, $conditions, $params = array())
 	{
-		return $this->joinInternal('left join', $table, $conditions, $params);
+		return $this->joinInternal('LEFT JOIN', $table, $conditions, $params);
 	}
 
 	/**
@@ -849,7 +633,7 @@ class Command extends \yii\base\Component
 	 */
 	public function rightJoin($table, $conditions, $params = array())
 	{
-		return $this->joinInternal('right join', $table, $conditions, $params);
+		return $this->joinInternal('RIGHT JOIN', $table, $conditions, $params);
 	}
 
 	/**
@@ -864,7 +648,7 @@ class Command extends \yii\base\Component
 	 */
 	public function crossJoin($table)
 	{
-		return $this->joinInternal('cross join', $table);
+		return $this->joinInternal('CROSS JOIN', $table);
 	}
 
 	/**
@@ -879,7 +663,7 @@ class Command extends \yii\base\Component
 	 */
 	public function naturalJoin($table)
 	{
-		return $this->joinInternal('natural join', $table);
+		return $this->joinInternal('NATURAL JOIN', $table);
 	}
 
 	/**
@@ -891,48 +675,13 @@ class Command extends \yii\base\Component
 	 * @return Command the command object itself
 	 * @since 1.1.6
 	 */
-	public function group($columns)
+	public function groupBy($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)$column;
-				elseif (strpos($column, '(') === false)
-					$columns[$i] = $this->_connection->quoteColumnName($column);
-			}
-			$this->_query['group'] = implode(', ', $columns);
-		}
+		$this->query->groupBy = $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 $conditions the conditions to be put after HAVING.
 	 * Please refer to {@link where} on how to specify conditions.
@@ -942,34 +691,12 @@ class Command extends \yii\base\Component
 	 */
 	public function having($conditions, $params = array())
 	{
-		$this->_query['having'] = $this->processConditions($conditions);
-		foreach ($params as $name => $value)
-			$this->params[$name] = $value;
+		$this->query->having = $conditions;
+		$this->query->addParams($params);
 		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 $columns the columns (and the directions) to be ordered by.
 	 * Columns can be specified in either a string (e.g. "id ASC, name DESC") or an array (e.g. array('id ASC', 'name DESC')).
@@ -978,89 +705,26 @@ class Command extends \yii\base\Component
 	 * @return Command the command object itself
 	 * @since 1.1.6
 	 */
-	public function order($columns)
+	public function orderBy($columns)
 	{
-		if (is_string($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)$column;
-				elseif (strpos($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);
-		}
+		$this->query->orderBy = $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 $offset the offset
 	 * @return Command the command object itself
 	 * @since 1.1.6
 	 */
-	public function limit($limit, $offset = null)
+	public function limit($limit)
 	{
-		$this->_query['limit'] = (int)$limit;
-		if ($offset !== null)
-			$this->offset($offset);
+		$this->query->limit = $limit;
 		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 $offset the offset
 	 * @return Command the command object itself
@@ -1068,32 +732,11 @@ class Command extends \yii\base\Component
 	 */
 	public function offset($offset)
 	{
-		$this->_query['offset'] = (int)$offset;
+		$this->query->offset = $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 $sql the SQL statement to be appended using UNION
 	 * @return Command the command object itself
@@ -1101,34 +744,8 @@ class Command extends \yii\base\Component
 	 */
 	public function union($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;
+		$this->query->union[] = $sql;
+		return $this->query;
 	}
 
 	/**
@@ -1141,28 +758,8 @@ class Command extends \yii\base\Component
 	 */
 	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);
+		$sql = $this->connection->getQueryBuilder()->insert($table, $columns, $params);
+		return $this->setSql($sql)->execute($params);
 	}
 
 	/**
@@ -1178,25 +775,8 @@ class Command extends \yii\base\Component
 	 */
 	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);
+		$sql = $this->connection->getQueryBuilder()->update($table, $columns, $conditions, $params);
+		return $this->setSql($sql)->execute($params);
 	}
 
 	/**
@@ -1210,10 +790,8 @@ class Command extends \yii\base\Component
 	 */
 	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);
+		$sql = $this->connection->getQueryBuilder()->delete($table, $conditions);
+		return $this->setSql($sql)->execute($params);
 	}
 
 	/**
@@ -1235,7 +813,8 @@ class Command extends \yii\base\Component
 	 */
 	public function createTable($table, $columns, $options = null)
 	{
-		return $this->setText($this->getConnection()->getSchema()->createTable($table, $columns, $options))->execute();
+		$sql = $this->connection->getQueryBuilder()->createTable($table, $columns, $options);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1247,7 +826,8 @@ class Command extends \yii\base\Component
 	 */
 	public function renameTable($table, $newName)
 	{
-		return $this->setText($this->getConnection()->getSchema()->renameTable($table, $newName))->execute();
+		$sql = $this->connection->getQueryBuilder()->renameTable($table, $newName);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1258,7 +838,8 @@ class Command extends \yii\base\Component
 	 */
 	public function dropTable($table)
 	{
-		return $this->setText($this->getConnection()->getSchema()->dropTable($table))->execute();
+		$sql = $this->connection->getQueryBuilder()->dropTable($table);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1269,11 +850,8 @@ class Command extends \yii\base\Component
 	 */
 	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;
+		$sql = $this->connection->getQueryBuilder()->truncateTable($table);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1288,7 +866,8 @@ class Command extends \yii\base\Component
 	 */
 	public function addColumn($table, $column, $type)
 	{
-		return $this->setText($this->getConnection()->getSchema()->addColumn($table, $column, $type))->execute();
+		$sql = $this->connection->getQueryBuilder()->addColumn($table, $column, $type);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1300,7 +879,8 @@ class Command extends \yii\base\Component
 	 */
 	public function dropColumn($table, $column)
 	{
-		return $this->setText($this->getConnection()->getSchema()->dropColumn($table, $column))->execute();
+		$sql = $this->connection->getQueryBuilder()->dropColumn($table, $column);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1313,7 +893,8 @@ class Command extends \yii\base\Component
 	 */
 	public function renameColumn($table, $name, $newName)
 	{
-		return $this->setText($this->getConnection()->getSchema()->renameColumn($table, $name, $newName))->execute();
+		$sql = $this->connection->getQueryBuilder()->renameColumn($table, $name, $newName);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1328,7 +909,8 @@ class Command extends \yii\base\Component
 	 */
 	public function alterColumn($table, $column, $type)
 	{
-		return $this->setText($this->getConnection()->getSchema()->alterColumn($table, $column, $type))->execute();
+		$sql = $this->connection->getQueryBuilder()->alterColumn($table, $column, $type);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1346,7 +928,8 @@ class Command extends \yii\base\Component
 	 */
 	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();
+		$sql = $this->connection->getQueryBuilder()->addForeignKey($name, $table, $columns, $refTable, $refColumns, $delete, $update);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1358,7 +941,8 @@ class Command extends \yii\base\Component
 	 */
 	public function dropForeignKey($name, $table)
 	{
-		return $this->setText($this->getConnection()->getSchema()->dropForeignKey($name, $table))->execute();
+		$sql = $this->connection->getQueryBuilder()->dropForeignKey($name, $table);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1373,7 +957,8 @@ class Command extends \yii\base\Component
 	 */
 	public function createIndex($name, $table, $column, $unique = false)
 	{
-		return $this->setText($this->getConnection()->getSchema()->createIndex($name, $table, $column, $unique))->execute();
+		$sql = $this->connection->getQueryBuilder()->createIndex($name, $table, $column, $unique);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1385,78 +970,8 @@ class Command extends \yii\base\Component
 	 */
 	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 $conditions;
-		elseif ($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)));
+		$sql = $this->connection->getQueryBuilder()->dropIndex($name, $table);
+		return $this->setSql($sql)->execute();
 	}
 
 	/**
@@ -1474,25 +989,8 @@ class Command extends \yii\base\Component
 	 */
 	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;
+		$this->query->join[] = array($type, $table, $conditions);
+		$this->query->addParams($params);
 		return $this;
 	}
 }
diff --git a/framework/db/dao/Connection.php b/framework/db/dao/Connection.php
index edea75b..2d4b8a7 100644
--- a/framework/db/dao/Connection.php
+++ b/framework/db/dao/Connection.php
@@ -460,6 +460,11 @@ class Connection extends \yii\base\ApplicationComponent
 		}
 	}
 
+	public function getQueryBuilder()
+	{
+		return $this->getSchema()->getQueryBuilder();
+	}
+
 	/**
 	 * Returns the ID of the last inserted row or sequence value.
 	 * @param string $sequenceName name of the sequence object (required by some DBMS)
diff --git a/framework/db/dao/DataReader.php b/framework/db/dao/DataReader.php
index 663f526..d2228d8 100644
--- a/framework/db/dao/DataReader.php
+++ b/framework/db/dao/DataReader.php
@@ -8,6 +8,8 @@
  * @license http://www.yiiframework.com/license/
  */
 
+namespace yii\db\dao;
+
 /**
  * DataReader represents a forward-only stream of rows from a query result set.
  *
diff --git a/framework/db/dao/Query.php b/framework/db/dao/Query.php
index 691dbda..cf96ad1 100644
--- a/framework/db/dao/Query.php
+++ b/framework/db/dao/Query.php
@@ -16,7 +16,7 @@ namespace yii\db\dao;
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */
-class Query extends CComponent
+class Query extends \yii\base\Component
 {
 	/**
 	 * @var mixed the columns being selected. This refers to the SELECT clause in an SQL
@@ -72,7 +72,7 @@ class Query extends CComponent
 	 * @var array list of query parameter values indexed by parameter placeholders.
 	 * For example, <code>array(':name'=>'Dan', ':age'=>31)</code>.
 	 */
-	public $params;
+	public $params = array();
 
 	public $union;
 
@@ -82,6 +82,18 @@ class Query extends CComponent
 		return $connection->getQueryBuilder()->build($this);
 	}
 
+	public function addParams($params)
+	{
+		foreach ($params as $name => $value) {
+			if (is_integer($name)) {
+				$this->params[] = $value;
+			}
+			else {
+				$this->params[$name] = $value;
+			}
+		}
+	}
+
 	/**
 	 * Appends a condition to the existing {@link condition}.
 	 * The new condition and the existing condition will be concatenated via the specified operator
@@ -361,157 +373,6 @@ class Query extends CComponent
 	}
 
 	/**
-	 * Merges with another criteria.
-	 * In general, the merging makes the resulting criteria more restrictive.
-	 * For example, if both criterias have conditions, they will be 'AND' together.
-	 * Also, the criteria passed as the parameter takes precedence in case
-	 * two options cannot be merged (e.g. LIMIT, OFFSET).
-	 * @param Query $criteria the criteria to be merged with.
-	 * @param boolean $useAnd whether to use 'AND' to merge condition and having options.
-	 * If false, 'OR' will be used instead. Defaults to 'AND'. This parameter has been
-	 * available since version 1.0.6.
-	 * @since 1.0.5
-	 */
-	public function mergeWith($criteria, $useAnd = true)
-	{
-		$and = $useAnd ? 'AND' : 'OR';
-		if (is_array($criteria))
-			$criteria = new self($criteria);
-		if ($this->select !== $criteria->select)
-		{
-			if ($this->select === '*')
-				$this->select = $criteria->select;
-			elseif ($criteria->select !== '*')
-			{
-				$select1 = is_string($this->select) ? preg_split('/\s*,\s*/', trim($this->select), -1, PREG_SPLIT_NO_EMPTY) : $this->select;
-				$select2 = is_string($criteria->select) ? preg_split('/\s*,\s*/', trim($criteria->select), -1, PREG_SPLIT_NO_EMPTY) : $criteria->select;
-				$this->select = array_merge($select1, array_diff($select2, $select1));
-			}
-		}
-
-		if ($this->condition !== $criteria->condition)
-		{
-			if ($this->condition === '')
-				$this->condition = $criteria->condition;
-			elseif ($criteria->condition !== '')
-				$this->condition = "( {$this->condition}) $and ( {$criteria->condition})";
-		}
-
-		if ($this->params !== $criteria->params)
-			$this->params = array_merge($this->params, $criteria->params);
-
-		if ($criteria->limit > 0)
-			$this->limit = $criteria->limit;
-
-		if ($criteria->offset >= 0)
-			$this->offset = $criteria->offset;
-
-		if ($criteria->alias !== null)
-			$this->alias = $criteria->alias;
-
-		if ($this->order !== $criteria->order)
-		{
-			if ($this->order === '')
-				$this->order = $criteria->order;
-			elseif ($criteria->order !== '')
-				$this->order = $criteria->order . ', ' . $this->order;
-		}
-
-		if ($this->group !== $criteria->group)
-		{
-			if ($this->group === '')
-				$this->group = $criteria->group;
-			elseif ($criteria->group !== '')
-				$this->group .= ', ' . $criteria->group;
-		}
-
-		if ($this->join !== $criteria->join)
-		{
-			if ($this->join === '')
-				$this->join = $criteria->join;
-			elseif ($criteria->join !== '')
-				$this->join .= ' ' . $criteria->join;
-		}
-
-		if ($this->having !== $criteria->having)
-		{
-			if ($this->having === '')
-				$this->having = $criteria->having;
-			elseif ($criteria->having !== '')
-				$this->having = "( {$this->having}) $and ( {$criteria->having})";
-		}
-
-		if ($criteria->distinct > 0)
-			$this->distinct = $criteria->distinct;
-
-		if ($criteria->together !== null)
-			$this->together = $criteria->together;
-
-		if ($criteria->index !== null)
-			$this->index = $criteria->index;
-
-		if (empty($this->scopes))
-			$this->scopes = $criteria->scopes;
-		elseif (!empty($criteria->scopes))
-		{
-			$scopes1 = (array)$this->scopes;
-			$scopes2 = (array)$criteria->scopes;
-			foreach ($scopes1 as $k => $v)
-			{
-				if (is_integer($k))
-					$scopes[] = $v;
-				elseif (isset($scopes2[$k]))
-					$scopes[] = array($k => $v);
-				else
-					$scopes[$k] = $v;
-			}
-			foreach ($scopes2 as $k => $v)
-			{
-				if (is_integer($k))
-					$scopes[] = $v;
-				elseif (isset($scopes1[$k]))
-					$scopes[] = array($k => $v);
-				else
-					$scopes[$k] = $v;
-			}
-			$this->scopes = $scopes;
-		}
-
-		if (empty($this->with))
-			$this->with = $criteria->with;
-		elseif (!empty($criteria->with))
-		{
-			$this->with = (array)$this->with;
-			foreach ((array)$criteria->with as $k => $v)
-			{
-				if (is_integer($k))
-					$this->with[] = $v;
-				elseif (isset($this->with[$k]))
-				{
-					$excludes = array();
-					foreach (array('joinType', 'on') as $opt)
-					{
-						if (isset($this->with[$k][$opt]))
-							$excludes[$opt] = $this->with[$k][$opt];
-						if (isset($v[$opt]))
-							$excludes[$opt] = ($opt === 'on' && isset($excludes[$opt]) && $v[$opt] !== $excludes[$opt]) ?
-								"($excludes[$opt]) AND $v[$opt]" : $v[$opt];
-						unset($this->with[$k][$opt]);
-						unset($v[$opt]);
-					}
-					$this->with[$k] = new self($this->with[$k]);
-					$this->with[$k]->mergeWith($v, $useAnd);
-					$this->with[$k] = $this->with[$k]->toArray();
-					if (count($excludes) !== 0)
-						$this->with[$k] = CMap::mergeArray($this->with[$k], $excludes);
-				}
-				else
-					$this->with[$k] = $v;
-			}
-		}
-	}
-
-	/**
 	 * @return array the array representation of the criteria
 	 * @since 1.0.6
 	 */
diff --git a/framework/db/dao/QueryBuilder.php b/framework/db/dao/QueryBuilder.php
index c32a429..f26118b 100644
--- a/framework/db/dao/QueryBuilder.php
+++ b/framework/db/dao/QueryBuilder.php
@@ -42,7 +42,7 @@ class QueryBuilder extends \yii\base\Component
 
 	public function __construct($schema)
 	{
-		$this->connection = $schema->getDbConnection();
+		$this->connection = $schema->connection;
 		$this->schema = $schema;
 	}
 
@@ -59,8 +59,98 @@ class QueryBuilder extends \yii\base\Component
 			$this->buildOrderBy($query),
 			$this->buildLimit($query),
 		);
+		$sql = implode("\n", array_filter($clauses));
+		if ($this->connection->tablePrefix !== null && strpos($sql, '{') !== false) {
+			$sql = preg_replace('/{{(.*?)}}/', $this->connection->tablePrefix . '\1', $sql);
+		}
+		return $sql;
+	}
+
+	/**
+	 * 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();
+		$count = 0;
+		foreach ($columns as $name => $value) {
+			$names[] = $this->schema->quoteColumnName($name);
+			if ($value instanceof Expression) {
+				$placeholders[] = $value->expression;
+				foreach ($value->params as $n => $v) {
+					$params[$n] = $v;
+				}
+			}
+			else {
+				$placeholders[] = ':p' . $count;
+				$params[':p' . $count] = $value;
+				$count++;
+			}
+		}
+
+		return 'INSERT INTO ' . $this->schema->quoteTableName($table)
+			. ' (' . implode(', ', $names) . ') VALUES ('
+			. implode(', ', $placeholders) . ')';
+	}
+
+	/**
+	 * 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();
+		$count = 0;
+		foreach ($columns as $name => $value) {
+			if ($value instanceof Expression) {
+				$lines[] = $this->schema->quoteSimpleColumnName($name) . '=' . $value->expression;
+				foreach ($value->params as $n => $v) {
+					$params[$n] = $v;
+				}
+			}
+			else {
+				$lines[] = $this->schema->quoteSimpleColumnName($name) . '=:p' . $count;
+				$params[':p' . $count] = $value;
+				$count++;
+			}
+		}
+		$sql = 'UPDATE ' . $this->schema->quoteTableName($table) . ' SET ' . implode(', ', $lines);
+		if (($where = $this->buildCondition($conditions)) != '') {
+			$sql .= ' WHERE ' . $where;
+		}
+
+		return $sql;
+	}
 
-		return implode("\n", array_filter($clauses));
+	/**
+	 * 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 = '')
+	{
+		$sql = 'DELETE FROM ' . $this->schema->quoteTableName($table);
+		if (($where = $this->buildCondition($conditions)) != '') {
+			$sql .= ' WHERE ' . $where;
+		}
+		return $sql;
 	}
 
 	/**
@@ -101,7 +191,7 @@ class QueryBuilder extends \yii\base\Component
 	 */
 	public function renameTable($table, $newName)
 	{
-		return 'RENAME TABLE ' . $this->quoteTableName($table) . ' TO ' . $this->quoteTableName($newName);
+		return 'RENAME TABLE ' . $this->schema->quoteTableName($table) . ' TO ' . $this->schema->quoteTableName($newName);
 	}
 
 	/**
@@ -111,7 +201,7 @@ class QueryBuilder extends \yii\base\Component
 	 */
 	public function dropTable($table)
 	{
-		return "DROP TABLE " . $this->quoteTableName($table);
+		return "DROP TABLE " . $this->schema->quoteTableName($table);
 	}
 
 	/**
@@ -121,7 +211,7 @@ class QueryBuilder extends \yii\base\Component
 	 */
 	public function truncateTable($table)
 	{
-		return "TRUNCATE TABLE " . $this->quoteTableName($table);
+		return "TRUNCATE TABLE " . $this->schema->quoteTableName($table);
 	}
 
 	/**
@@ -136,8 +226,8 @@ class QueryBuilder extends \yii\base\Component
 	 */
 	public function addColumn($table, $column, $type)
 	{
-		return 'ALTER TABLE ' . $this->quoteTableName($table)
-			. ' ADD ' . $this->quoteColumnName($column) . ' '
+		return 'ALTER TABLE ' . $this->schema->quoteTableName($table)
+			. ' ADD ' . $this->schema->quoteColumnName($column) . ' '
 			. $this->getColumnType($type);
 	}
 
@@ -150,8 +240,8 @@ class QueryBuilder extends \yii\base\Component
 	 */
 	public function dropColumn($table, $column)
 	{
-		return "ALTER TABLE " . $this->quoteTableName($table)
-			. " DROP COLUMN " . $this->quoteSimpleColumnName($column);
+		return "ALTER TABLE " . $this->schema->quoteTableName($table)
+			. " DROP COLUMN " . $this->schema->quoteSimpleColumnName($column);
 	}
 
 	/**
@@ -164,9 +254,9 @@ class QueryBuilder extends \yii\base\Component
 	 */
 	public function renameColumn($table, $name, $newName)
 	{
-		return "ALTER TABLE " . $this->quoteTableName($table)
-			. " RENAME COLUMN " . $this->quoteSimpleColumnName($name)
-			. " TO " . $this->quoteSimpleColumnName($newName);
+		return "ALTER TABLE " . $this->schema->quoteTableName($table)
+			. " RENAME COLUMN " . $this->schema->quoteSimpleColumnName($name)
+			. " TO " . $this->schema->quoteSimpleColumnName($newName);
 	}
 
 	/**
@@ -180,9 +270,9 @@ class QueryBuilder extends \yii\base\Component
 	 */
 	public function alterColumn($table, $column, $type)
 	{
-		return 'ALTER TABLE ' . $this->quoteTableName($table) . ' CHANGE '
-			. $this->quoteSimpleColumnName($column) . ' '
-			. $this->quoteSimpleColumnName($column) . ' '
+		return 'ALTER TABLE ' . $this->schema->quoteTableName($table) . ' CHANGE '
+			. $this->schema->quoteSimpleColumnName($column) . ' '
+			. $this->schema->quoteSimpleColumnName($column) . ' '
 			. $this->getColumnType($type);
 	}
 
@@ -202,14 +292,14 @@ class QueryBuilder extends \yii\base\Component
 	{
 		$columns = preg_split('/\s*,\s*/', $columns, -1, PREG_SPLIT_NO_EMPTY);
 		foreach ($columns as $i => $col)
-			$columns[$i] = $this->quoteColumnName($col);
+			$columns[$i] = $this->schema->quoteColumnName($col);
 		$refColumns = preg_split('/\s*,\s*/', $refColumns, -1, PREG_SPLIT_NO_EMPTY);
 		foreach ($refColumns as $i => $col)
-			$refColumns[$i] = $this->quoteColumnName($col);
-		$sql = 'ALTER TABLE ' . $this->quoteTableName($table)
-			. ' ADD CONSTRAINT ' . $this->quoteColumnName($name)
+			$refColumns[$i] = $this->schema->quoteColumnName($col);
+		$sql = 'ALTER TABLE ' . $this->schema->quoteTableName($table)
+			. ' ADD CONSTRAINT ' . $this->schema->quoteColumnName($name)
 			. ' FOREIGN KEY (' . implode(', ', $columns) . ')'
-			. ' REFERENCES ' . $this->quoteTableName($refTable)
+			. ' REFERENCES ' . $this->schema->quoteTableName($refTable)
 			. ' (' . implode(', ', $refColumns) . ')';
 		if ($delete !== null)
 			$sql .= ' ON DELETE ' . $delete;
@@ -226,8 +316,8 @@ class QueryBuilder extends \yii\base\Component
 	 */
 	public function dropForeignKey($name, $table)
 	{
-		return 'ALTER TABLE ' . $this->quoteTableName($table)
-			. ' DROP CONSTRAINT ' . $this->quoteColumnName($name);
+		return 'ALTER TABLE ' . $this->schema->quoteTableName($table)
+			. ' DROP CONSTRAINT ' . $this->schema->quoteColumnName($name);
 	}
 
 	/**
@@ -248,11 +338,11 @@ class QueryBuilder extends \yii\base\Component
 			if (strpos($col, '(') !== false)
 				$cols[] = $col;
 			else
-				$cols[] = $this->quoteColumnName($col);
+				$cols[] = $this->schema->quoteColumnName($col);
 		}
 		return ($unique ? 'CREATE UNIQUE INDEX ' : 'CREATE INDEX ')
-			. $this->quoteTableName($name) . ' ON '
-			. $this->quoteTableName($table) . ' (' . implode(', ', $cols) . ')';
+			. $this->schema->quoteTableName($name) . ' ON '
+			. $this->schema->quoteTableName($table) . ' (' . implode(', ', $cols) . ')';
 	}
 
 	/**
@@ -263,7 +353,7 @@ class QueryBuilder extends \yii\base\Component
 	 */
 	public function dropIndex($name, $table)
 	{
-		return 'DROP INDEX ' . $this->quoteTableName($name) . ' ON ' . $this->quoteTableName($table);
+		return 'DROP INDEX ' . $this->schema->quoteTableName($name) . ' ON ' . $this->schema->quoteTableName($table);
 	}
 
 	/**
@@ -330,6 +420,9 @@ class QueryBuilder extends \yii\base\Component
 	protected function buildSelect($query)
 	{
 		$select = $query->distinct ? 'SELECT DISTINCT' : 'SELECT';
+		if ($query->selectOption != '') {
+			$select .= ' ' . $query->selectOption;
+		}
 
 		$columns = $query->select;
 		if (empty($columns)) {
@@ -408,7 +501,7 @@ class QueryBuilder extends \yii\base\Component
 					}
 					$joins[$i] = strtoupper($join[0]) . ' ' . $table;
 					if (isset($join[2])) {  // join condition
-						$condition = $this->processCondition($join[2]);
+						$condition = $this->buildCondition($join[2]);
 						$joins[$i] .= ' ON ' . $condition;
 					}
 				}
@@ -423,7 +516,7 @@ class QueryBuilder extends \yii\base\Component
 
 	protected function buildWhere($query)
 	{
-		$where = $this->processConditions($query->where);
+		$where = $this->buildCondition($query->where);
 		return empty($where) ? '' : 'WHERE ' . $where;
 	}
 
@@ -453,7 +546,7 @@ class QueryBuilder extends \yii\base\Component
 
 	protected function buildHaving($query)
 	{
-		$having = $this->processConditions($query->having);
+		$having = $this->buildCondition($query->having);
 		return empty($having) ? '' : 'HAVING ' . $having;
 	}
 
@@ -515,7 +608,7 @@ class QueryBuilder extends \yii\base\Component
 		return "UNION (\n" . implode("\n) UNION (\n", $unions) . "\n)";
 	}
 
-	protected function processCondition($conditions)
+	protected function buildCondition($conditions)
 	{
 		if (!is_array($conditions)) {
 			return $conditions;
@@ -529,7 +622,7 @@ class QueryBuilder extends \yii\base\Component
 		if ($operator === 'OR' || $operator === 'AND') {
 			$parts = array();
 			for ($i = 1; $i < $n; ++$i) {
-				$condition = $this->processCondition($conditions[$i]);
+				$condition = $this->buildCondition($conditions[$i]);
 				if ($condition !== '') {
 					$parts[] = '(' . $condition . ')';
 				}