[英]MySQL query with multiple subqueries is too slow. How do I speed it up?
我有一个MySQL查询,它完全可以执行我想要的操作,但是需要110到130秒之间的任何时间进行处理。 问题是它与在查询后20秒钟后超时的软件协同工作。
我可以做些什么来加快查询速度? 我正在考虑将数据库移至另一台服务器,但是在走那条路线之前,还有其他更优雅的选择吗?
-- 1 Give me a list of IDs & eBayItemIDs
-- 2 where it is flagged as bottom tier
-- 3 Where it has been checked less than 168 times
-- 4 Where it has not been checked in the last hour
-- 5 Or where it was never checked but appears on the master list.
-- 1 Give me a list of IDs & eBayItemIDs
SELECT `id`, eBayItemID
FROM `eBayDD_Main`
-- 2 where it is flagged as bottom tier
WHERE `isBottomTier`='0'
-- 3 Where it has been checked less than 168 times
AND (`id` IN
(SELECT `mainid`
FROM `eBayDD_History`
GROUP BY `mainid`
HAVING COUNT(`mainID`) < 168)
-- 4 Where it has not been checked in the last hour
AND id IN
(SELECT `mainID`
FROM `eBayDD_History`
GROUP BY `mainID`
HAVING ((TIME_TO_SEC(TIMEDIFF(NOW(), MAX(`dateCollected`)))/60)/60) > 1))
-- 5 Or where it was never checked but appears on the master list.
OR (`id` IN
(SELECT `id`
FROM `eBayDD_Main`)
AND `id` NOT IN
(SELECT `mainID`
FROM `eBayDD_History`))
如果我正确理解该逻辑,则应该可以用以下代码替换此逻辑:
select m.`id`, m.eBayItemID
from `eBayDD_Main` m left outer join
(select `mainid`, count(`mainID`) as cnt,
TIME_TO_SEC(TIMEDIFF(NOW(), MAX(`dateCollected`)))/60)/60) as dc
from `eBayDD_History`
group by `mainid`
) hm
on m.mainid = hm.mainid
where m.`isBottomTier` = '0' and hm.cnt < 168 and hm.dc > 1 or
hm.mainid is null;
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