/**
* 从库查询SQL
* @param $sql
* @param $key
* @param int $mode
* @return array
*/
private function sql($sql, $key = null, $mode = self::FETCH_TYPE_ALL)
{
$dns = is_array($this->dbConfig) ? $this->dbConfig[1] : $this->dbConfig;
return TXDatabase::instance($dns)->sql($sql, $key, $mode);
}