Mysql中group by的问题。。

问题描述

问 题

Mysql中，下面这样的写法是可以允许的。但是严不严谨，支不支持这样写？有疑惑过不去这个坎，请大家帮忙看看。

select * from user group by user_name;

解决方案

最详细的文档说明在官网找到了。

MySQL 5.7.5 and up implements detection of functional dependence. If the ONLY_FULL_GROUP_BY SQL mode is enabled (which it is by default), MySQL rejects queries for which the select list, HAVING condition, or ORDER BY list refer to nonaggregated columns that are neither named in the GROUP BY clause nor are functionally dependent on them. (Before 5.7.5, MySQL does not detect functional dependency and ONLY_FULL_GROUP_BY is not enabled by default. For a description of pre-5.7.5 behavior, see the MySQL 5.6 Reference Manual.)

来源：https://dev.mysql.com/doc/ref...

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