How to do equivalent of "limit distinct"?

How can I limit a result set to n distinct values of a given column(s), where the actual number of rows may be higher?

Input table:

client_id, employer_id, other_value
1, 2, abc
1, 3, defg
2, 3, dkfjh
3, 1, ldkfjkj
4, 4, dlkfjk
4, 5, 342
4, 6, dkj
5, 1, dlkfj
6, 1, 34kjf
7, 7, 34kjf
8, 6, lkjkj
8, 7, 23kj

desired output, where limit distinct=5 distinct values of client_id:

1, 2, abc
1, 3, defg
2, 3, dkfjh
3, 1, ldkfjkj
4, 4, dlkfjk
4, 5, 342
4, 6, dkj
5, 1, dlkfj

Platform this is intended for is MySQL.

From stackoverflow

• You can use a subselect

  select * from table where client_id in 
  (select distinct client_id from table order by client_id limit 5)
  

  ʞɔıu : I think this is right but I'll leave the question open for a little while to see if anyone else has a better answer

• This is for SQL Server. I can't remember, MySQL may use a LIMIT keyword instead of TOP. That may make the query more efficient if you can get rid of the inner most subquery by using the LIMIT and DISTINCT in the same subquery. (It looks like Vinko used this method and that LIMIT is correct. I'll leave this here for the second possible answer though.)

  SELECT
       client_id,
       employer_id,
       other_value
  FROM
       MyTable
  WHERE
       client_id IN
       (
            SELECT TOP 5
                 client_id
            FROM
            (
                 SELECT DISTINCT
                      client_id
                 FROM
                      MyTable
            ) SQ
            ORDER BY
                 client_id
       )
  

  Of course, add in your own WHERE clause and ORDER BY clause in the subquery.

  Another possibility (compare performance and see which works out better) is:

  SELECT
       client_id,
       employer_id,
       other_value
  FROM
       MyTable T1
  WHERE
       T1.code IN
       (
            SELECT
                 T2.code
            FROM
                 MyTable T2
            WHERE
                 (SELECT COUNT(*) FROM MyTable T3 WHERE T3,code < T2.code) < 5
       )