在执行sql语句时，如果用了group by会提示以下错误
```
select id,product_type,count(*) from product group by product_type
> 1055 - Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'product.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
> 时间: 0s
```
什么原因
>MySql从5.7版本开始默认开启only_full_group_by规则，规则核心原则如下，没有遵循原则的sql会被认为是不合法的sql。
```
1、order by后面的列必须是在select后面存在的。
2、 select、having或order by后面存在的非聚合列必须全部在group by中存在
```
解决方法
```
show variables like '%sql_mode%';`
以下为mysql显示
variable_name value
sql_mode ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION
执行
set session sql_mode ='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION';
show variables like '%sql_mode%';
select id,product_type,count(*) from hl_product group by product_type;
```
或者在mysql.ini中加入
`sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION'`
然后重启mysql服务器
