问题描述
我有时在我的sql查询中互换使用NOT IN和NOT EXIST，并且两者都产生相同的结果. NOT EXIST背后的逻辑与NOT IN相同吗?因为我认为NOT IN ...(在子查询中被评估为或")等于NOT EXIST(也被评估为或")?还是我想念什么?
I sometimes interchanged the use of NOT IN and NOT EXIST in my sql queries and both yield the same result. Is the logic behind the NOT EXIST the same as NOT IN? Because I think that NOT IN... (is being evaluated as "OR" inside the subqueries) is equal to NOT EXIST (which is also evaluated as "OR")? Or am i missing something?
推荐答案
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简而言之，NOT IN与NOT EXISTS在两个处理子查询返回的NULL值的方式上稍有不同.
In a nutshell, NOT IN is slightly different from NOT EXISTS in the way the two handle NULL values returned by the subquery.
如果没有NULL值，它们都对NESTED LOOP ANTI JOIN执行某种操作，但是NOT IN效率更高.
If there are no NULL values, they both perform a kind on NESTED LOOP ANTI JOIN, but NOT IN is a little bit more efficient.
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