MySQL-SELECT WHERe字段IN（子查询）-为什么极慢？

正在为每行运行子查询，因为它是一个相关查询。通过从子查询中选择所有内容，可以将相关查询变成不相关查询，如下所示：

SELECt * FROM(    SELECt relevant_field    FROM some_table    GROUP BY relevant_field    HAVINg COUNT(*) > 1) AS subquery

最终查询如下所示：

SELECt *FROM some_tableWHERe relevant_field IN(    SELECt * FROM    (        SELECt relevant_field        FROM some_table        GROUP BY relevant_field        HAVINg COUNT(*) > 1    ) AS subquery)