SQL优化技巧 - IN子查询优化
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Optimize your SQL Queries by Clicks!
问题定义
为了获取最近一年内有订单的用户信息，可以使用以下的三种写法去实现，它们在语义上是等价的。那它们的性能如何？如何对它们进行优化？这是本文讨论的问题。
- Query1 - IN子查询(
= ANY)
select * from customer where c_custkey in (select o_custkey from orders where O_ORDERDATE>=current_date - interval 1 year)
- Query2 - EXISTS子查询
select * from customer where exists (select * from orders where c_custkey = o_custkey and O_ORDERDATE>=current_date - interval 1 year)