使用EXISTS(或NOT EXISTS)通常将提高查询的效率，由于NOT IN子句将对子查询中的表执行了一个全表遍历。
oracle在执行IN子查询过程中，先执行子查询结果放入临时表再进行主查询； 而exists先运行主查询，再执行子查询查到第一个匹配项 如：查询 A表中没有和B表或C表相连的数据 select A.id,A.reads,A.addtime from A where A.person_id not in (select user_id from B ) or A.worksite_id not in (select id from C) order by A.addtime desc 程序执行时间：40109.38毫秒 select A.id,A.reads,A.addtime from A where not exists (select id FROM B where B.user_id=A.person_id) or not exists (select id FROM C where C.id=A.worksite_id) order by Sendorder.addtime desc 程序执行时间：8531.25毫秒
ms ssql 实例：
select subscriber_id from NewsLetterSystem_CampaignCategorySubscriber ccs WITH ( NOLOCK ) where NOT EXISTS( SELECT distinct subscriber_id FROM NewsLetterSystem_OpenTracking ot WITH ( NOLOCK ) WHERE ot.subscriber_id=ccs.subscriber_id and ot.campaign_id = 52801) and ccs.campaign_id = 52801 and ccs.status_id = 1
转载于:https://www.cnblogs.com/zoro-zero/p/7454263.html
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