MySQL 8中的sql_mode中的默认值如下：
mysql> select @@sql_mode\G
*************************** 1. row ***************************
@@sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION
1 row in set (0.00 sec)
sql_mode的配置中ONLY_FULL_GROUP_BY是开发人员最容易遇到坑，这个设置对SQL语句的要求是：出现在select字段后面的只能是group by后面的分组字段，或使用聚合函数包裹着的字段。
例如下面的SQL语句在select的字段中增加了一个不是group by后的字段后将出错：
mysql> select staff_id , max(amount) from payment group by staff_id;
+----------+-------------+
| staff_id | max(amount) |
+----------+-------------+
| 1 | 11.99 |
| 2 | 11.99 |
+----------+-------------+
2 rows in set (0.04 sec)
mysql> select rental_id, staff_id , max(amount) from payment group by staff_id;
ERROR 1055 (42000): Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'sakila.payment.rental_id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
mysql>
遇到这种错误可以修改SQL语句解决，也可以修改sql_mode，去掉其中的ONLY_FULL_GROUP_BY，例如：
mysql> select @@sql_mode;
+------------+
| @@sql_mode |
+------------+
| |
+------------+
1 row in set (0.00 sec)
mysql> select rental_id, staff_id , max(amount) from payment group by staff_id;
+-----------+----------+-------------+
| rental_id | staff_id | max(amount) |
+-----------+----------+-------------+
| 76 | 1 | 11.99 |
| 1422 | 2 | 11.99 |
+-----------+----------+-------------+
2 rows in set (0.19 sec)
