MySQL duration for 9 rows, that's my code - mysql

Question

SELECT DATE_FORMAT(b.checktime,"%Y-%m-%d") AS dtDate,
case when (
SELECT DATE_FORMAT(a.checktime,'%H:%i:%s')
FROM checkinout a
WHERE a.checktype='0'
and a.userid=1
and DATE_FORMAT(a.checktime,'%Y-%m-%d')=DATE_FORMAT(b.checktime,'%Y-%m-%d')
LIMIT 1)
is not NULL
then
(
SELECT
DATE_FORMAT(a.checktime,'%H:%i:%s')
FROM checkinout a
WHERE a.checktype='0'
and a.userid=1
and DATE_FORMAT(a.checktime,'%Y-%m-%d')=DATE_FORMAT(b.checktime,'%Y-%m-%d')
LIMIT 1
)
else 'N/A' END
AS Chkin
from checkinout b
where
DATE_FORMAT(b.checktime,"%m")='06' AND
DATE_FORMAT(b.checktime,"%Y")='2019' AND
DATE_FORMAT(b.checktime,"%w")!='0' AND .
DATE_FORMAT(b.checktime,"%w")!='6' AND .
DATE_FORMAT(b.checktime,"%Y-%m-%d") not in
(select date_s from wend)
GROUP BY dtDate
ORDER BY dtDate DESC
Affected rows: 0 Found rows: 9 Warnings: 0 Duration for 1 query: 25.665 sec.
what's wrong with this query, for 9 rows need 25.665 seconds
Thanks

Answer 1

Without understanding the purpose of the query, it can be rewritten to:
SELECT DISTINCT date(b.checktime) AS dtDate,
coalesce((
SELECT time(a.checktime)
FROM checkinout a
WHERE a.checktype = '0'
and a.userid = 1
and date(a.checktime) = date(b.checktime)
LIMIT 1
), 'N/A') AS Chkin
from checkinout b
where month(b.checktime) = 6
AND year(b.checktime) = 2019
AND weekday(b.checktime) not in (5, 6) -- non weekend
AND date(b.checktime) not in (select date_s from wend)
ORDER BY dtDate DESC
Though GROUP BY might perform better than DISTINCT - You should test both. However, the above query can be optimized to use indexes.
The outer condition month(b.checktime) = 6 AND year(b.checktime) = 2019 can be rewritten to b.checktime >= '2019-06-01' AND b.checktime < '2019-06-01' + INTERVAL 1 MONTH. This way the engine should be able to use an index on (checktime).
The condition date(a.checktime) = date(b.checktime) can be written as a.checktime >= date(b.checktime) and a.checktime < date(b.checktime) + INTERVAL 1 DAY. Here I suggest one of the following indexes: (checktype, userid, checktime), (userid, checktype, checktime) or (userid, checktime).
And for date(b.checktime) not in (select date_s from wend) it might be better to use an "anti-join".
So here is the final query, which I would try:
SELECT DISTINCT date(b.checktime) AS dtDate,
coalesce((
SELECT time(a.checktime)
FROM checkinout a
WHERE a.checktype = '0'
and a.userid = 1
and a.checktime >= date(b.checktime)
and a.checktime < date(b.checktime) + INTERVAL 1 DAY
LIMIT 1
), 'N/A') AS Chkin
from checkinout b
LEFT JOIN wend w ON w.date_s = date(b.checktime)
where b.checktime >= '2019-06-01'
AND b.checktime < '2019-06-01' + INTERVAL 1 MONTH
AND weekday(b.checktime) not in (5, 6) -- non weekend
AND w.date_s IS NULL
ORDER BY dtDate DESC