php 根据父级ID查询出全部子级

private static function recursion($res)
{
    $output = array();
    foreach ($res as $k => $v)
    {
        $sql = "select * from broad_category WHERE pid=".$v['id'];
        $tmpRes = Yii::$app->db->createCommand($sql)->queryAll();
        $output []= $v;
        if (!empty($tmpRes))
        {
            $output = array_merge($output, self::recursion($tmpRes));
        }
    }
    return $output;
}