MySQL records count with condition

问题

I need to get records count of table «posts» where votes>=5 to create pagination.

tables:

table «posts»: user_id, post_n, visibility, type

visibility values: 0, 1, 2; type values: 'text', 'photo' … (it`s enum field, have 6 values)

table «votes»: vote_n, post_n, voter_id, vote

vote values: -1 or 1

query:

SELECT post_n, (SELECT SUM(vote) FROM votes WHERE votes.post_n=posts.post_n)AS votes
FROM posts WHERE visibility=2 AND type='text' HAVING votes>=5

time 0.4039

Is it possible to optimize it?

回答1:

I think you would get better results without a subquery. You could do this by using GROUP BY:

SELECT p.post_n AS post_n, SUM(v.vote) AS votes
FROM posts p
INNER JOIN votes v ON (v.post_n = p.post_n)
WHERE p.visibility = 2 AND p.type = 'text'
GROUP BY p.post_n
HAVING SUM(v.vote) >= 5

来源：https://stackoverflow.com/questions/3749831/mysql-records-count-with-condition