mysql循环查询语句请教？？

Question

数据库是mysql5的
表users
user_id  user_name  parent_id 
       1               user1         0
        2              user2         0
       3              user3          1
       4             userf0          3
        5            user8           3
       23          usercc          1 
现在要求user_id为 1 的用户下面的用户数（包含下级的下级）结果应该为 user_id  (3,4,5,23) 
??这种查询怎样写？？？

Answer 1

http://blog.csdn.net/acmain_chm/article/details/4142971