MySQL认为子查询不是派生的！

2022-01-23 00:00:00 sql subquery mysql

EXPLAIN SELECT node_id 
          FROM node 
         WHERE person_id IN (SELECT person_id 
                               FROM user 
                              WHERE is_locked = 0);

MySql 中的结果告诉我子查询是派生的.但事实并非如此！

Results in MySql telling me the subquery is derived. But it's not!

(我知道这很容易被重写为 JOIN，但我想知道为什么 MySQL 认为这是一个依赖子查询.)

(I know this could easily be re-written as a JOIN, but I want to know why MySQL thinks this is a dependent subquery.)

推荐答案

这是 MySQL 查询优化器中的一个错误.看起来，如果子查询中的表与主查询中的表匹配，即使它显然不应该是，它也被视为依赖子查询，并且没有简单的修复.对不起;去参加吧.

This is a bug in the MySQL Query Optimizer. It would seem that, if the table in the subquery matches the table in the main query, it is considered a dependent subquery even if it obviously should not be, and there's no easy fix. Sorry; go for the join.

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