Sql Merging multiple records into one record

Question

I have table with two columns user_id and tags.

  user_id    tags
    1    
    1    
    1    

        

Answer 1

duplicate of https://stackoverflow.com/questions/16218616/sql-marching-values-in-column-a-with-more-than-1-value-in-column-b/16218678#16218678

select user_id, group_concat(tags separator ',')
from t
group by user_id