MySQL中具有父id的多用户级别

我有如下4级用户表

user_id parent_id
1       NULL
2       1
3       2
4       2
5       3
6       1

我想选择某个父id下的所有用户，例如，user_id=1，在这种情况下，将返回如下结果：

user_id  parent_id
2        1         // return because parent_id = 1
6        1         // return because parent_id = 1
3        2         // return because parent_id of 2 is 1
4        2         // return because parent_id of 2 is 1
5        3         // return because parent_id of 3 is 2

通过提供id，查询将是什么

提前谢谢

试试这个：

    Select 
user_id 
from 

my_table 
where parent_id in 
(
Select 
user_id 
from my_table where parent_id in 
(Select user_id from my_table where parent_id in(Select user_id from my_table where parent_id =?)))

检查此项：：

parentid as refid 
Select userid  from SampleTree where refid = 0 or refid in (Select userid from SampleTree where refid =0 
or refid in (Select userid from SampleTree where refid =0 or
refid in (Select userid from SampleTree where refid =0)))