MySQL的sql_mode解析与设置

Posted 2020-10-28 fireporsche

参考地址： http://blog.csdn.net/ccccalculator/article/details/70432123

因为在mysql中使用group by 是总是出现1055的错误，这就导致了必须去查看是什么原因了，查询了相关的资料，现在将笔记记录下来，以便后面可以参考使用：

sql_mode:简而言之就是：它定义了你MySQL应该支持的sql语法，对数据的校验等等

select @@sql_mode:使用该命令我们可以查看我们当前数据库的sql_mode

mysql> select @@sql_mode;
+-------------------------------------------------------------------------------------------------------------------------------------------+
| @@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)

下面我们来看看sql_mode的各个值的含义：

ONLY_FULL_GROUP_BY：

对于GROUP BY聚合操作，如果在SELECT中的列，没有在GROUP BY中出现，那么将认为这个SQL是不合法的，因为列不在GROUP BY从句中

因为有only_full_group_by，所以我们要在MySQL中正确的使用group by语句的话，只能是select column1 from tb1 group by column1(即只能展示group by的字段，其他均都要报1055的错)

实例：

mysql> select * from tt1;
+----+-------+--------+
| id | name  | gender |
+----+-------+--------+
|  1 | xiong |      0 |
|  2 | ying  |      0 |
|  3 | cai   |      0 |
|  4 | zhang |      0 |
|  5 | li    |      1 |
|  6 | wang  |      1 |
+----+-------+--------+
6 rows in set (0.00 sec)

mysql> select id,name from tt1 group by name;
ERROR 1055 (42000):

mysql> select * from tt1;
+----+-------+--------+
| id | name  | gender |
+----+-------+--------+
|  1 | xiong |      0 |
|  2 | ying  |      0 |
|  3 | cai   |      0 |
|  4 | zhang |      0 |
|  5 | li    |      1 |
|  6 | wang  |      1 |
+----+-------+--------+
6 rows in set (0.00 sec)
mysql> select * from tt1 group by name;
ERROR 1055 (42000):

mysql> select * from tt1;
+----+-------+--------+
| id | name  | gender |
+----+-------+--------+
|  1 | xiong |      0 |
|  2 | ying  |      0 |
|  3 | cai   |      0 |
|  4 | zhang |      0 |
|  5 | li    |      1 |
|  6 | wang  |      1 |
+----+-------+--------+
6 rows in set (0.00 sec)
mysql> select name from tt1 group by name;
+-------+
| name  |
+-------+
| cai   |
| li    |
| wang  |
| xiong |
| ying  |
| zhang |
+-------+
6 rows in set (0.00 sec)

所以我们要使用能正确的使用group by 的话就必须删除掉only_full_group_by

set sql_mode=(select replace(@@sql_mode,‘ONLY_FULL_GROUP_BY‘,‘‘)); 可以使用该语句来将空格替换掉only_full_group_by，这样我们就可以使用

mysql> SET sql_mode=(SELECT REPLACE(@@sql_mode,‘ONLY_FULL_GROUP_BY‘,‘‘));
Query OK, 0 rows affected (0.00 sec)

mysql> select id,name from tt1 group by name;
+----+-------+
| id | name  |
+----+-------+
|  3 | cai   |
|  5 | li    |
|  6 | wang  |
|  1 | xiong |
|  2 | ying  |
|  4 | zhang |
+----+-------+
6 rows in set (0.00 sec)

mysql> SET sql_mode=(SELECT REPLACE(@@sql_mode,‘ONLY_FULL_GROUP_BY‘,‘‘));
Query OK, 0 rows affected (0.00 sec)
mysql> select * from tt1 group by name;
+----+-------+--------+
| id | name  | gender |
+----+-------+--------+
|  3 | cai   |      0 |
|  5 | li    |      1 |
|  6 | wang  |      1 |
|  1 | xiong |      0 |
|  2 | ying  |      0 |
|  4 | zhang |      0 |
+----+-------+--------+
6 rows in set (0.00 sec)

但是这种方法只是做了暂时的修改，我们可以更改配置文件my.ini

sql_mode= "STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"