mysql - Sql Merging multiple records into one record -

i have table 2 columns user_id , tags.

  user_id    tags     1    <tag1><tag4>     1    <tag1><tag2>     1    <tag3><tag2>     2    <tag1><tag2>     2    <tag4><tag5>     3    <tag4><tag1>     3    <tag4><tag1>     4    <tag1><tag2> 

i want merge 2 records 1 record this.

  user_id    tags     1    tag1, tag2, tag3, tag4     2    tags, tag2, tag4, tag5     3    tag4, tag1     4    tag1, tag2 

how can this? can me out. need convert tags field array []. don't have knowledge on typical sql commads. know basics. ruby on rails guy.

you should group_concat function in mysql.a example here

in case like:

select user_id, group_concat(tags) tablename group user_id