MySQL limit maximum rows for same "user" value

Question

How can I limit in MySQL maximum rows for the same "user" value?

id | user | data

Answer 1

I think that it's ok, You may want to make a

select count(1) from table where user='XXX'

and check the count before performing the insert.

Answer 2

This could be done by using special "dual" table:

INSERT INTO table (id, user, data)
    SELECT 1, 'XXX', 'somedata' 
      FROM dual 
     WHERE NOT EXISTS (
         SELECT user
           FROM t
          WHERE user = 'XXX'
       GROUP BY user 
         HAVING COUNT(*) >= 5
     )