Oracle IN 与 Exists 的区别?

2021-12-06 00:00:00 sql oracle

我对 oracle IN 和 EXISTS 感到困惑.我有以下要求.

I am confused with oracle IN and EXISTS. I have below requirement.

我需要得到名字在-的所有员工

I need to get all the employees whose names are in-

select * from emp where ename in('smith','brown','john','johnson');

我可以在这里使用 EXISTS 吗?IN 子句也有 1000 个限制.EXISTS 是否也有这样的限制?

Can i use EXISTS here? Also IN clause has 1000 limitation. Does EXISTS also has any such limitation?

谢谢！

推荐答案

IN 选择匹配值的列表.EXISTS 返回布尔值，如真或假.Exists 比 in 快.

IN picks the list of matching values. EXISTS returns the boolean values like true or false. Exists is faster than in.

示例

输入

select ename from emp e where mgr in(select empno from emp where ename='KING');

存在

select ename from emp e where exists (select 1 from emp where e.mgr = empno and ename = 'KING');

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