使用NOT IN表示多个表

Question

如何简化多个"不在"查询？使用多个子查询是否有效:不在(...)和不在(..)和不在(...)

我正在使用计数(抱歉忘记了)

 Select count (VisitorID)

 from Company

 where VisitorID not in (select VisitorID from UserLog where ActionID = 2 )

 and VisitorID not in (select VisitorID from Supplies where productID = 4)

Answer 1

Select count (VisitorID)

from Company C
where
NOT EXISTS (select * from UserLog U where ActionID = 2 AND C.VisitorID  = U.VisitorID)
AND
NOT EXISTS (select * from Supplies S where productID = 4 AND S.VisitorID  = U.VisitorID)

为什么不存在？

• NOT IN:UserLog或Supplies中的任何NULL VisitorID值表示不匹配

• (LEFT JOIN):如果每个VisitorID有许多UserLog或Supplies,则为多个输出行.需要DISTINCT改变计划

通常,NOT EXISTS是唯一正确的选项