mysql : query three times on the same table - mysql

Question

I am currently writing a query.
Retrieves information from users, posts, and additional information tables in posts (post_views_info).
SELECT
u.email,
u.user_nm,
p.pid,
p.post_ttl,
p.date,
p.ref_level,
p.ref_origin,
p.ref_step,
date(p.date) = date(now()) AS is_today,
(SELECT category_path FROM post_category WHERE category_id = p.category_id) as category_full_path,
(SELECT COUNT(*) FROM post_status_info AS sub_i WHERE sub_i.pid = p.pid AND sub_i.status = 'A') AS recommendCount,
(SELECT COUNT(*) FROM post_status_info AS sub_i WHERE sub_i.pid = p.pid AND sub_i.status = 'B') AS oppositeCount,
(SELECT COUNT(*) FROM post_status_info AS sub_i WHERE sub_i.pid = p.pid AND sub_i.status = 'C') AS reportCount
FROM
(
SELECT *
FROM post as p
WHERE
p.is_enable = 1
ORDER BY
p.ref_origin DESC,
p.ref_step ASC
) as p,
user AS u
WHERE
p.uid = u.uid
ORDER BY
ref_origin DESC,
ref_step ASC
In the above query, we query the same table three times to get the number of posts 'A', 'B', 'C'.
To solve this problem, I changed the query as follows.
SELECT
u.email,
u.user_nm,
p.pid,
p.post_ttl,
p.date,
p.ref_level,
p.ref_origin,
psi.reportCount,
psi.recommendCount,
psi.oppositeCount,
p.ref_step,
date(p.date) = date(now()) AS is_today,
(SELECT category_path FROM post_category WHERE category_id = p.category_id) as category_full_path
FROM
user AS u,
(
SELECT *
FROM post as p
WHERE
p.is_enable = 1
ORDER BY
p.ref_origin DESC,
p.ref_step ASC
LIMIT 0, 15
) as p left join
(
SELECT
pid,
COUNT(if(status = 'A', 1, null)) AS reportCount,
COUNT(if(status = 'B', 1, null)) AS recommendCount,
COUNT(if(status = 'C', 1, null)) AS oppositeCount
FROM post_status_info
group by pid
) AS psi
on
psi.pid = p.pid
WHERE
p.uid = u.uid
ORDER BY
ref_origin DESC,
ref_step ASC
I think it would be better to query the same table three times.
Which code is better in terms of performance?
Thanks.

Answer 1

I think second option is more fruitful in terms of performance. Because here we have less number of queries to execute.
You can also do it by using CASE.
SELECT
u.email,
u.user_nm,
p.pid,
p.post_ttl,
p.date,
p.ref_level,
p.ref_origin,
p.ref_step,
date(p.date) = date(now()) AS is_today,
(SELECT category_path FROM post_category WHERE category_id = p.category_id) as category_full_path,
(SUM(CASE WHEN sub_i.status = 'A' THEN 1 ELSE 0 END)) AS recommendCount,
(SUM(CASE WHEN sub_i.status = 'B' THEN 1 ELSE 0 END)) AS oppositeCount,
(SUM(CASE WHEN sub_i.status = 'C' THEN 1 ELSE 0 END)) AS reportCount
FROM
(
SELECT *
FROM post as p
WHERE
p.is_enable = 1
ORDER BY
p.ref_origin DESC,
p.ref_step ASC
) as p,
INNER JOIN user AS u ON u.uid = p.uid
INNER JOIN post_status_info as sub_i ON p.pid = sub_i.pid
GROUP BY p.pid
ORDER BY
ref_origin DESC,
ref_step ASC