mysql - Subquery returns more than 1 row, Error 1242 -

i new mysql, can guys please me in this?

query:

update users u,        posts p set    u.tags = (select group_concat(tags)                    (select distinct tags,                                          user_id                            posts                          group  tags,                                    user_id) p                  group  user_id)  u.user_id = p.user_id;  

error:

error 1242 (21000): subquery returns more 1 row 

you need correlated subquery:

update users u    set u.tags =(select group_concat(distinct tags)                 posts p                 p.user_id = u.user_id                 group user_id )  

i'm not sure query doing. has join on outside unnecessary. grouping tags , user_id on inside, unnecessary distinct keyword. subquery producing different value each user_id, no wonder getting error of many rows returned. set statement can have 1 value.