Question

I have this table:

id
feed_id
...

Let’s say that I have 500 rows and I want to select 3 entries for each feed_id? And 50 as total limit.

How to write this SQL?

Answer 1

Use:

SELECT x.feedid
  FROM (SELECT t.feedid,
               CASE WHEN @feed != t.feedid THEN @rownum := 1 ELSE @rownum := @rownum + 1 END AS rank,
               @feed := t.feedid
          FROM TABLE t
          JOIN (SELECT @rownum := NULL, @feed := 0) r
      ORDER BY t.feedid) x
 WHERE x.rank <= 3
 ORDER BY x.feedid
 LIMIT 50

What’s not clear is the details of what you want returned – all the rows in your table, or just the feedid.