MySQL 5.7.20
输入:
mysql> select * from SC group by Sid;
输出结果:
ERROR 1055 (42000): Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'school_db.SC.Cid' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
ONLY_FULL_GROUP_BY的意思是:对于GROUP BY聚合操作,如果在SELECT中的列,没有在GROUP BY中出现,那么这个SQL是不合法的,因为列不在GROUP BY从句中,也就是说查出来的列必须在group by后面出现否则就会报错,或者这个字段出现在聚合函数里面。
SELECT @@GLOBAL.sql_mode;
SELECT @@SESSION.sql_mode;
输出:
mysql> SELECT @@GLOBAL.sql_mode;
+-------------------------------------------------------------------------------------------------------------------------------------------+
| @@GLOBAL.sql_mode |
+-------------------------------------------------------------------------------------------------------------------------------------------+
| ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> SELECT @@SESSION.sql_mode;
+-------------------------------------------------------------------------------------------------------------------------------------------+
| @@SESSION.sql_mode |
+-------------------------------------------------------------------------------------------------------------------------------------------+
| ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
第一项默认开启ONLY_FULL_GROUP_BY了,导致出现了错误,需要把它的默认关掉。
这两个mode进行修改:
SET GLOBAL sql_mode ='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';
SET SESSION sql_mode ='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';
设置好之后,使用group by就不会出现之前的错误啦