Question

I’m using a query which generally executes in under a second, but sometimes takes between 10-40 seconds to finish. I’m actually not totally clear on how the subquery works, I just know that it works, in that it gives me 15 rows for each faverprofileid.

I’m logging slow queries and it’s telling me 5823244 rows were examined, which is odd because there aren’t anywhere close to that many rows in any of the tables involved (the favorites table has the most at 50,000 rows).

Can anyone offer me some pointers? Is it an issue with the subquery and needing to use filesort?

EDIT: Running explain shows that the users table is not using an index (even though id is the primary key). Under extra it says: Using temporary; Using filesort.

SELECT F.id,F.created,U.username,U.fullname,U.id,I.*    FROM favorites AS F   INNER JOIN users AS U ON F.faver_profile_id = U.id   INNER JOIN items AS I ON F.notice_id = I.id   WHERE faver_profile_id IN (360,379,95,315,278,1)   AND F.removed = 0   AND I.removed = 0    AND F.collection_id is null    AND I.nudity = 0   AND (SELECT COUNT(*) FROM favorites WHERE faver_profile_id = F.faver_profile_id   AND created > F.created AND removed = 0 AND collection_id is null) < 15  ORDER BY F.faver_profile_id, F.created DESC; 

Answer 1

I think with GROUP BY and HAVING it should be faster. Is that what you want?

SELECT F.id,F.created,U.username,U.fullname,U.id, I.field1, I.field2, count(*) as CNT FROM favorites AS F   INNER JOIN users AS U ON F.faver_profile_id = U.id   INNER JOIN items AS I ON F.notice_id = I.id   WHERE faver_profile_id IN (360,379,95,315,278,1)   AND F.removed = 0   AND I.removed = 0    AND F.collection_id is null    AND I.nudity = 0   GROUP BY F.id,F.created,U.username,U.fullname,U.id,I.field1, I.field2 HAVING CNT < 15 ORDER BY F.faver_profile_id, F.created DESC; 

Don’t know which fields from items you need, so I’ve put placeholders.