Question

What I’m trying to do is speed up this query. Currently it’s about 15+ seconds slow. There are indexes on both r.email and v.sent as well as r.id, r.viewed and r.saved. EXPLAIN is showing both keys are in use, however I’m seeing that it’s using Using where; Using temporary; Using filesort.

Any ideas on improving this query?

SELECT r.id, r.top, r.email
FROM request as r
WHERE r.viewed = 0 AND r.saved = 0 AND r.email NOT IN ( 
    SELECT v.sent FROM viewing as v WHERE v.sent = r.email
)
GROUP BY r.email 
ORDER BY r.top desc, r.date
LIMIT 100;

Answer 1

MySQL uses a temporary table for multiple records in an IN clause. Try

SELECT r.id, r.top, r.email
FROM request as r
left outer join viewing v on v.sent = r.email
WHERE r.viewed = 0 AND r.saved = 0 AND v.sent is null
GROUP BY r.email 
ORDER BY r.top desc, r.date
LIMIT 100;