具有多个子查询的 MySQL 查询太慢。我怎样才能加快速度？

Question

我有一个 MySQL 查询，它完全符合我的要求，但处理时间在 110 到 130 秒之间。问题是它与一个软件协同工作，该软件在查询后 20 秒就会超时。

有什么办法可以加快查询速度吗？我正在考虑将数据库移至另一台服务器，但在走这条路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`))

Answer 1

如果我正确理解了逻辑，您应该能够用以下逻辑替换此逻辑:

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;