mysql中的sql_mode

mysql数据库的中有一个环境变量sql_mode,定义了mysql应该支持的sql语法，数据校验等！我们可以通过以下方式查看当前数据库使用的sql_mode：

mysql> select @@sql_mode;
+----------------------------------------------------------------+
| @@sql_mode                                                     |
+----------------------------------------------------------------+
| STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+----------------------------------------------------------------+ 

mysql5.0以上版本支持三种sql_mode模式

ANSI模式	宽松模式，对插入数据进行校验，如果不符合定义类型或长度，对数据类型调整或截断保存，报warning警告。
TRADITIONAL模式	严格模式，当向mysql数据库插入数据时，进行数据的严格校验，保证错误数据不能插入，报error错误。用于事物时，会进行事物的回滚。
STRICT_TRANS_TABLES模式	严格模式，进行数据的严格校验，错误数据不能插入，报error错误。

1 ANSI模式

在ANSI模式下，当我们插入数据时，未满足列长度要求时，数据同样会插入成功，但是对超出列长度的字段进行截断，同时报告warning警告。 

mysql> set @@sql_mode=ANSI;
Query OK, 0 rows affected (0.00 sec)  

mysql> create table test(name varchar(4), pass varchar(4));
Query OK, 0 rows affected (0.03 sec)  

mysql> insert into test values('aaaaa','aaaaa'),('bbbb','bbbb');
Query OK, 2 rows affected, 2 warnings (0.02 sec)
Records: 2  Duplicates: 0  Warnings: 2  

mysql> show warnings;
+---------+------+-------------------------------------------+
| Level   | Code | Message                                   |
+---------+------+-------------------------------------------+
| Warning | 1265 | Data truncated for column 'name' at row 1 |
| Warning | 1265 | Data truncated for column 'pass' at row 1 |
+---------+------+-------------------------------------------+
2 rows in set (0.00 sec)  

mysql> select * from test;
+------+------+
| name | pass |
+------+------+
| aaaa | aaaa |
| bbbb | bbbb |
+------+------+
2 rows in set (0.00 sec)

2 STRICT_TRANS_TABLES模式

在STRICT_TRANS_TABLES模式下，当我们插入数据时，mysql会严格的进行数据的校验，当发现插入列值未满足要求，直接报告error错误，保证了错误数据无法插入到数据库中。

mysql> set @@sql_mode=STRICT_TRANS_TABLES;
Query OK, 0 rows affected (0.00 sec)  

mysql> create table test(name varchar(4), pass varchar(4));
Query OK, 0 rows affected (0.02 sec)  

mysql> insert into test values('aaaaa','aaaaa'),('bbbb','bbbb');
ERROR 1406 (22001): Data too long for column 'name' at row 1  

mysql> show errors;
+-------+------+------------------------------------------+
| Level | Code | Message                                  |
+-------+------+------------------------------------------+
| Error | 1406 | Data too long for column 'name' at row 1 |
+-------+------+------------------------------------------+
1 row in set (0.00 sec)  

mysql> select * from test;
Empty set (0.00 sec)  

3 TRADITIONAL模式，初看结果是不是一样

mysql> set @@sql_mode=TRADITIONAL;
Query OK, 0 rows affected (0.00 sec)  

mysql> create table test(name varchar(4), pass varchar(4));
Query OK, 0 rows affected (0.02 sec)  

mysql> insert into test values('aaaaa','aaaaa'),('bbbb','bbbb');
ERROR 1406 (22001): Data too long for column 'name' at row 1  

mysql> show errors;
+-------+------+------------------------------------------+
| Level | Code | Message                                  |
+-------+------+------------------------------------------+
| Error | 1406 | Data too long for column 'name' at row 1 |
+-------+------+------------------------------------------+
1 row in set (0.00 sec)  

mysql> select * from test;
Empty set (0.00 sec)  

但是，可以看看设置后的情况

mysql> set @@sql_mode=TRADITIONAL;
Query OK, 0 rows affected (0.00 sec)

mysql> select @@sql_mode\G
*************************** 1. row ***************************
@@sql_mode: STRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,TRADITIONAL,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
1 row in set (0.00 sec)

在TRADITIONAL模式下，对所有的事务存储引擎，非事务存储引擎检查，日期类型中的月和日部分不能包含0，不能有0这样的日期(0000-00-00),数据不能除0，禁止grant自动创建新用户等一些校验。

最后：

set @@只是在sessions级别设置的，要想所有的都生效，还是要设置配置文件

vi /etc/my.cnf

在[mysqld]下面添加如下列：

sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

#NO_ENGINE_SUBSTITUTION对于不存在的引擎就报错，不加的话，指定不支持的引擎时指定默认的innodb

另外：sql_mode还有一个配置ONLY_FULL_GROUP_BY，这个表示采用group by帅选数据的时候只能查看新组内信息

改模式之前的操作
mysql> select * from employee group by post;
+----+--------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name   | sex    | age | hire_date  | post                                    | post_comment | salary     | office | depart_id |
+----+--------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 14 | 张野   | male   |  28 | 2016-03-11 | operation                               | NULL         |   10000.13 |    403 |         3 |
|  9 | 歪歪   | female |  48 | 2015-03-11 | sale                                    | NULL         |    3000.13 |    402 |         2 |
|  2 | alex   | male   |  78 | 2015-03-02 | teacher                                 | NULL         | 1000000.31 |    401 |         1 |
|  1 | egon   | male   |  18 | 2017-03-01 | 老男孩驻沙河办事处外交大使              | NULL         |    7300.33 |    401 |         1 |
+----+--------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
4 rows in set (0.00 sec)

此时的sql_mode:

mysql> select @@sql_mode;
+----------------------------------------------------------------+
| @@sql_mode                                                     |
+----------------------------------------------------------------+
| STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+----------------------------------------------------------------+
1 row in set (0.00 sec)

修改一下，退出再进入才会生效

mysql> set global sql_mode='STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION,ONLY_FULL_GROUP_BY';
Query OK, 0 rows affected (0.00 sec)

mysql> select @@sql_mode;
+----------------------------------------------------------------+
| @@sql_mode                                                     |
+----------------------------------------------------------------+
| STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> exit
Bye
再次进入

mysql> select @@sql_mode;
+-----------------------------------------------------------------------------------+
| @@sql_mode |
+-----------------------------------------------------------------------------------+
| ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-----------------------------------------------------------------------------------+
1 row in set (0.00 sec)

下面查看修改后的查看结果

mysql> select * from employee group by post;   //只能查看post
ERROR 1055 (42000): 't1.employee.id' isn't in GROUP BY
mysql> select post from employee group by post;
+-----------------------------------------+
| post                                    |
+-----------------------------------------+
| operation                               |
| sale                                    |
| teacher                                 |
| 老男孩驻沙河办事处外交大使              |
+-----------------------------------------+
4 rows in set (0.00 sec)

mysql> select id,post from employee group by post;
ERROR 1055 (42000): 't1.employee.id' isn't in GROUP BY

mysql> select name,post from employee group by post,name;  //根据group by 后面的选择查看
+------------+-----------------------------------------+
| name | post |
+------------+-----------------------------------------+
| 张野 | operation |
| 程咬金 | operation |
| 程咬铁 | operation |
| 程咬铜 | operation |
| 程咬银 | operation |
| 丁丁 | sale |
| 丫丫 | sale |
| 星星 | sale |
| 格格 | sale |
| 歪歪 | sale |
| alex | teacher |
| jingliyang | teacher |
| jinxin | teacher |
| liwenzhou | teacher |
| wupeiqi | teacher |
| xiaomage | teacher |
| yuanhao | teacher |
| egon | 老男孩驻沙河办事处外交大使 |
+------------+-----------------------------------------+
18 rows in set (0.00 sec)