Query is slow while doing a NOT IN on a nested SELECT from another table
SELECT problems . * , users.id AS new_user_id, users.nick AS nick
FROM problems, users
WHERE problems.deleted =0
AND problems.topic_id =1
AND problems.user_id = users.id
AND problems.id NOT
IN (
SELECT DISTINCT (problem_id)
FROM problems_attempted
WHERE user_id =1
AND total_questions = ( attempted_right + attempted_wrong + s开发者_运维技巧kipped )
)
ORDER BY problems.updated DESC
Can this query be optimized for a better performance?
Nested queries are always a performance bottleneck. Try to use join instead
select p.*, u.*
from problems p join users u
on p.user_id = u.id
join problems_attempted pa on pa.problem_id = p.id
where not (pa.user_id = 1
and total_questions = ( attempted_right + attempted_wrong + skipped ))
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