当使用group by的语句中，select后面跟的列，在group by后面没有时，会报以下错误：

Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'XXX' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

这是MySQL8.0默认开启only_full_group_by模式导致的，该模式限定select后面跟的列，在group by后面必须要有。

解决方式一：该方式重启mysql会失效

1、查询sql_mode:

select @@session.sql_mode;

ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION

2、重新设置sql_mode，删除ONLY_FULL_GROUP_BY

set @@global.sql_mode = 'STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION'

解决方式二

修改配置文件my.cnf

找到my.cnf，添加一下配置：

sql_mode=STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION

重启mysql即可。
service mysqld restart