private function _prepareExpression()
	{
		$this->expression = ($this->tableName && $this->alias) ?
			$this->tableName . '.' . $this->columnName . ' AS ' . $this->alias : (($this->tableName && !$this->alias) ?
				$this->tableName . '.' . $this->columnName : ((!$this->tableName && $this->alias) ?
					$this->columnName . ' AS ' . $this->alias : $this->columnName));
	}