private function _prepareTables(array $tablesArray)
	{
		if(count($tablesArray) === 0)
		{
			throw new \Exception('"table"-method of the statement have to invoked before!');
		}

		$tables = ' ';
		foreach($tablesArray as $table)
		{
			$tables .= $table->getExpression() . ', ';
		}
		$tables       = substr($tables, 0, strlen($tables) - 2);
		$this->tables = $tables . ' ';
	}