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采坑之运用MySQL，SQL_MODE是什么坑

发布时间：09/01 来源：未知浏览：关键词：

SQL_MODE是MySQL中的一个系统变量（variable），可由多个MODE组成，每个MODE操纵一种行动，如可否同意除数为0，日期中可否同意'0000-00-00'值。

为什么需要关注SQL_MODE呢？

第一，看三个简便的Demo（MySQL 5.6）。

mysql> create table t1(c1 datetime);
Query OK, 0 rows affected (0.16 sec)

mysql> insert into t1 values('2019-02-29');
Query OK, 1 row affected, 1 warning (0.01 sec)

mysql> select * from t1;
+---------------------+
| c1                  |
+---------------------+
| 0000-00-00 00:00:00 |
+---------------------+
row in set (0.00 sec)

实际储备值与插入值不符。

mysql> create table t2(c1 varchar(10));
Query OK, 0 rows affected (0.06 sec)

mysql> insert into t2 values('a'),('b'),('c');
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from t2;
+------+
| c1   |
+------+
| a    |
| b    |
| c    |
+------+
rows in set (0.00 sec)

mysql> alter table t2 modify column c1 int;
Query OK, 3 rows affected, 3 warnings (0.05 sec)
Records: 3  Duplicates: 0  Warnings: 3

mysql> show warnings;
+---------+------+-------------------------------------------------------+
| Level   | Code | Message                                               |
+---------+------+-------------------------------------------------------+
| Warning | 1366 | Incorrect integer value: 'a' for column 'c1' at row 1 |
| Warning | 1366 | Incorrect integer value: 'b' for column 'c1' at row 2 |
| Warning | 1366 | Incorrect integer value: 'c' for column 'c1' at row 3 |
+---------+------+-------------------------------------------------------+
rows in set (0.00 sec)

mysql> select * from t2;
+------+
| c1   |
+------+
|    0 |
|    0 |
|    0 |
+------+
rows in set (0.00 sec)

DDL致使原列内容丧失。

mysql> create table t3(id int not null,c1 varchar(10));
Query OK, 0 rows affected (0.05 sec)

mysql> insert into t3 values(null,'a');
ERROR 1048 (23000): Column 'id' cannot be null

mysql> insert into t3(c1) values('a');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+-----------------------------------------+
| Level   | Code | Message                                 |
+---------+------+-----------------------------------------+
| Warning | 1364 | Field 'id' doesn't have a default value |
+---------+------+-----------------------------------------+
row in set (0.00 sec)

mysql> select * from t3;
+----+------+
| id | c1   |
+----+------+
|  0 | a    |
+----+------+
row in set (0.00 sec)

显式指定列和不显式指定的处置逻辑居然不一样。

为什么会这样呢？这个即与SQL_MODE有关。

在MySQL 5.6中， SQL_MODE的默许值为"NO_ENGINE_SUBSTITUTION"，非严厉模式。

在这种模式下，在停止数据变动操纵时，假如触及的列中存在无效值（如日期不存在，数据类型不合错误，数据溢出），只会提醒"Warning"，并不会报错。

假如要躲避上述问题，需开启SQL_MODE的严厉模式。

SQL_MODE的严厉模式

所谓的严厉模式，即SQL_MODE中开启了STRICT_ALL_TABLES或STRICT_TRANS_TAB LES。

还是上面的Demo，看看严厉模式下，MySQL的处置逻辑。

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

mysql> insert into t1 values('2019-02-29');
ERROR 1292 (22007): Incorrect datetime value: '2019-02-29' for column 'c1' at row 1

mysql> alter table t2 modify column c1 int;
ERROR 1366 (HY000): Incorrect integer value: 'a' for column 'c1' at row 1

mysql> insert into t3(c1) values('a');
ERROR 1364 (HY000): Field 'id' doesn't have a default value

一样的SQL，在严厉模式下，直接提醒"ERROR"，而不是"Warning"。

同是严厉模式，下面看看STRICT_ALL_TABLES或STRICT_TRAN S_TABLES的不同。

STRICT_ALL_TABLES与STRICT_TRANS_TABLES的不同

STRICT_TRANS_TABLES只对事务表开启严厉模式，STRICT_ALL_TABLES是对所有表开启严厉模式，不仅仅是事务表，还包罗非事务表。

看下面这个测试。

对myisam表插入3条数据，其中，第3条数据是空字符串，与定义的int类型不匹配。

mysql> create table t (c1 int) engine=myisam;
Query OK, 0 rows affected (0.00 sec)

mysql> set session sql_mode='STRICT_TRANS_TABLES';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into t values (1),(2),('');
Query OK, 3 rows affected, 1 warning (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 1

mysql> show warnings;
+---------+------+------------------------------------------------------+
| Level   | Code | Message                                              |
+---------+------+------------------------------------------------------+
| Warning | 1366 | Incorrect integer value: '' for column 'c1' at row 3 |
+---------+------+------------------------------------------------------+
row in set (0.00 sec)

mysql> select * from t;
+------+
| c1   |
+------+
|    1 |
|    2 |
|    0 |
+------+
rows in set (0.00 sec)

mysql> set session sql_mode='STRICT_ALL_TABLES';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into t values (1),(2),('');
ERROR 1366 (HY000): Incorrect integer value: '' for column 'c1' at row 3

可以看到，在表为myisam储备引擎的状况下，只要开启STRICT_ALL_TABLES才会报错。

不一样版本默许的SQL_MODE

MySQL 5.5：空

MySQL 5.6：NO_ENGINE_SUBSTITUTION

MySQL 5.7：ONLY_FULL_GROUP_BY, STRICT_TRANS_TABLES, NO_ZERO_IN_DATE, NO_ZERO_DATE, ERROR_FOR_pISION_BY_ZERO, NO_AUTO_CREATE_USER, NO_ENGINE_SUBSTITUTION

MySQL 8.0：ONLY_FULL_GROUP_BY, STRICT_TRANS_TABLES, NO_ZERO_IN_DATE, NO_ZERO_DATE, ERROR_FOR_pISION_BY_ZERO, NO_ENGINE_SUBSTITUTION

怎样修改SQL_MODE

SQL_MODE既可在全局级别修改，又可在会话级别修改。可指定多个MODE，MODE之间用逗号隔开。

全局级别

set global sql_mode='ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES';

会话级别

set session sql_mode='ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES';

SQL_MODE的完全列表

ALLOW_INVALID_DATES

在严厉模式下，关于日期的检测较为严厉，其必需有效。若开启该MODE，关于month和day的检测会相对宽松。其中，month只需在1~12之间，day只需在1~31之间，而不管其可否有效，如下面的'2004-02-31'。

mysql> create table t (c1 datetime);
Query OK, 0 rows affected (0.21 sec)

mysql> set session sql_mode='STRICT_TRANS_TABLES';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into t values('2004-02-31');
ERROR 1292 (22007): Incorrect datetime value: '2004-02-31' for column 'c1' at row 1

mysql> set session sql_mode='STRICT_TRANS_TABLES,ALLOW_INVALID_DATES';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into t values('2004-02-31');
Query OK, 1 row affected (0.01 sec)

mysql> select * from t;
+---------------------+
| c1 |
+---------------------+
| 2004-02-31 00:00:00 |
+---------------------+
row in set (0.00 sec)

留意，该MODE只适用于DATE和DATETIME，不适用于TIMESTAMP。

ANSI_QUOTES

在MySQL中，关于关键字和保存字，是不同意用做表名和字段名的。假如必然要使用，必需使用反引号（"`"）停止转义。

mysql> create table order (id int);
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'order (id int)' at line 1

mysql> create table `order` (id int);
Query OK, 0 rows affected (0.12 sec)

若开启该MODE，则双引号，同反引号一样，可对关键字和保存字转义。

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

mysql> create table "order" (c1 int);
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '"order" (c1 int)' at line 1

mysql> set session sql_mode='ANSI_QUOTES';
Query OK, 0 rows affected (0.00 sec)

mysql> create table "order" (c1 int);
Query OK, 0 rows affected (0.17 sec)

需要留意的是，在开启该MODE的状况下，不克不及再用双引号来引字符串。

ERROR_FOR_pISION_BY_ZERO

该MODE决议除数为0的处置逻辑，实际结果还取决于可否开启严厉模式。

1. 开启严厉模式，且开启该MODE，插入1/0，会直接报错。

mysql> create table t (c1 double);
Query OK, 0 rows affected (0.04 sec)

mysql> set session sql_mode='STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into t values(1/0);
ERROR 1365 (22012): Division by 0

2. 只开启严厉模式，不开启该MODE，同意1/0的插入，且不提醒warning，1/0最后会转化为NULL。

mysql> set session sql_mode='STRICT_TRANS_TABLES';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into t values(1/0);
Query OK, 1 row affected (0.07 sec)

mysql> select * from t;
+------+
| c1  |
+------+
| NULL |
+------+
row in set (0.00 sec)

3. 不开启严厉模式，只开启该MODE，同意1/0的插入，但提醒warning。

4. 不开启严厉模式，也不开启该MODE，同意1/0的插入，且不提醒warning，同2一样。

HIGH_NOT_PRECEDENCE

默许状况下，NOT的优先级低于比力运算符。但在某些低版本中，NOT的优先级高于比力运算符。

看看两者的不同。

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

mysql> select not 1 < -1;
+------------+
| not 1 < -1 |
+------------+
|          1 |
+------------+
row in set (0.00 sec)

mysql> set session sql_mode='HIGH_NOT_PRECEDENCE';
Query OK, 0 rows affected (0.00 sec)

mysql> select not 1 < -1;
+------------+
| not 1 < -1 |
+------------+
|          0 |
+------------+
row in set (0.00 sec)

在sql_mode为空的状况下， not 1 < -1相当于not (1 < -1)，假如设定了'HIGH_ NOT_PRECEDENCE'，则相当于(not 1) < -1。

IGNORE_SPACE

默许状况下，函数名和左括号（“(”）之间不同意存在空格。若开启该MODE，则同意。

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

mysql> select count(*) from t;
+----------+
| count(*) |
+----------+
|        2 |
+----------+
row in set (0.00 sec)

mysql> select count (*) from t;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '*) from t' at line 1

mysql> set session sql_mode='IGNORE_SPACE';
Query OK, 0 rows affected (0.01 sec)

mysql> select count (*) from t;
+-----------+
| count (*) |
+-----------+
|         2 |
+-----------+
row in set (0.01 sec)

NO_AUTO_VALUE_ON_ZERO

默许状况下，在对自增主键插入NULL或0时，会主动生成下一个值。若开启该MODE，当插入0时，并不会主动生成下一个值。

假如表中自增主键列存在0值，在停止逻辑备份复原时，大概会致使数据不一致。所以mysqldump在生成备份数据此前，会主动开启该MODE，以幸免数据不一致的状况。

mysql> create table t (id int auto_increment primary key);
Query OK, 0 rows affected (0.11 sec)

mysql> set session sql_mode='';
Query OK, 0 rows affected (0.01 sec)

mysql> insert into t values (0);
Query OK, 1 row affected (0.04 sec)

mysql> select * from t;
+----+
| id |
+----+
|  1 |
+----+
row in set (0.00 sec)

mysql> set session sql_mode='NO_AUTO_VALUE_ON_ZERO';
Query OK, 0 rows affected (0.02 sec)

mysql> insert into t values (0);
Query OK, 1 row affected (0.09 sec)

mysql> select * from t;
+----+
| id |
+----+
|  0 |
|  1 |
+----+
rows in set (0.00 sec)

NO_BACKSLASH_ESCAPES

默许状况下，反歪杠“\”会作为转义符，若开启该MODE，则反歪杠“\”会作为一个一般字符，而不是转义符。

mysql> set session sql_mode='';
Query OK, 0 rows affected (0.01 sec)

mysql> select '\\t';
+----+
| \t |
+----+
| \t |
+----+
row in set (0.00 sec)

mysql> set session sql_mode='NO_BACKSLASH_ESCAPES';
Query OK, 0 rows affected (0.00 sec)

mysql> select '\\t';
+-----+
| \\t |
+-----+
| \\t |
+-----+
row in set (0.00 sec)

NO_DIR_IN_CREATE

默许状况下，在创立表时，可以指定数据名目（DATA DIRECTORY）和索引名目（INDEX DIRECTORY），若开启该MODE，则会忽略这两个选项。在主从复制场景下，可在从库上开启该MODE。

mysql> set session sql_mode='';
Query OK, 0 rows affected (0.01 sec)

mysql> create table t (id int) data directory '/tmp/';
Query OK, 0 rows affected (0.15 sec)

mysql> show create table t\G
*************************** 1. row ***************************
      Table: t
Create Table: CREATE TABLE `t` (
  `id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci DATA DIRECTORY='/tmp/'
row in set (0.00 sec)

mysql> set session sql_mode='NO_DIR_IN_CREATE';
Query OK, 0 rows affected (0.00 sec)

mysql> drop table t;
Query OK, 0 rows affected (0.11 sec)

mysql> create table t (id int) data directory '/tmp/';
Query OK, 0 rows affected, 1 warning (0.05 sec)

mysql> show create table t\G
*************************** 1. row ***************************
      Table: t
Create Table: CREATE TABLE `t` (
  `id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
row in set (0.00 sec)

NO_ENGINE_SUBSTITUTION

在开启该MODE的状况下，在创立表时，假如指定的储备引擎不存在或不支撑，则会直接提醒“ERROR”。

若不开启，则只会提醒“Warning”，且使用默许的储备引擎。

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

mysql> create table t (id int) engine=federated;
Query OK, 0 rows affected, 2 warnings (0.11 sec)

mysql> show warnings;
+---------+------+-------------------------------------------+
| Level   | Code | Message                                   |
+---------+------+-------------------------------------------+
| Warning | 1286 | Unknown storage engine 'federated'        |
| Warning | 1266 | Using storage engine InnoDB for table 't' |
+---------+------+-------------------------------------------+
rows in set (0.00 sec)

mysql> show create table t\G
*************************** 1. row ***************************
      Table: t
Create Table: CREATE TABLE `t` (
  `id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
row in set (0.01 sec)

mysql> drop table t;
Query OK, 0 rows affected (0.11 sec)

mysql> set session sql_mode='NO_ENGINE_SUBSTITUTION';
Query OK, 0 rows affected (0.00 sec)

mysql> create table t (id int) engine=federated;
ERROR 1286 (42000): Unknown storage engine 'federated'

NO_UNSIGNED_SUBTRACTION

两个整数相减，假如其中一个数是无符号位，默许状况下，会发生一个无符号位的值，假如该值为负数，则会提醒“ERROR”。如，

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

mysql> select cast(0 as unsigned)-1;
ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '(cast(0 as unsigned) - 1)'

若开启该MODE，则同意结果为负数。

mysql> set session sql_mode='NO_UNSIGNED_SUBTRACTION';
Query OK, 0 rows affected (0.00 sec)

mysql> select cast(0 as unsigned)-1;
+-----------------------+
| cast(0 as unsigned)-1 |
+-----------------------+
|                    -1 |
+-----------------------+
row in set (0.00 sec)

NO_ZERO_DATE

该MODE会影响'0000-00-00'的插入。实际结果还取决于可否开启严厉模式。

1. 在开启严厉模式，且同时开启该MODE，是不同意'0000-00-00'插入的。

mysql> set session sql_mode='STRICT_TRANS_TABLES,NO_ZERO_DATE';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show warnings\G
*************************** 1. row ***************************
  Level: Warning
  Code: 3135
Message: 'NO_ZERO_DATE', 'NO_ZERO_IN_DATE' and 'ERROR_FOR_DIVISION_BY_ZERO' sql modes should be used with strict mode. They will be merged with strict mode in
a future release.1 row in set (0.00 sec)

mysql> insert into t values ('0000-00-00');
ERROR 1292 (22007): Incorrect datetime value: '0000-00-00' for column 'c1' at row 1

2. 只开启严厉模式，不开启该MODE，同意'0000-00-00'值的插入，且不提醒warning。

mysql> set session sql_mode='STRICT_TRANS_TABLES';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into t values ('0000-00-00');
Query OK, 1 row affected (0.04 sec)

3. 不开启严厉模式，只开启该MODE，同意'0000-00-00'值的插入，但提醒warning。

mysql> set session sql_mode='NO_ZERO_DATE';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into t values ('0000-00-00');
Query OK, 1 row affected, 1 warning (0.05 sec)

mysql> show warnings;
+---------+------+---------------------------------------------+
| Level   | Code | Message                                     |
+---------+------+---------------------------------------------+
| Warning | 1264 | Out of range value for column 'c1' at row 1 |
+---------+------+---------------------------------------------+
row in set (0.01 sec)

4. 不开启严厉模式，也不开启该MODE，同意'0000-00-00'值的插入，且不提醒warning。

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

mysql> insert into t values ('0000-00-00');
Query OK, 1 row affected (0.03 sec)

NO_ZERO_IN_DATE

同NO_ZERO_DATE相似，只不外NO_ZERO_DATE针对的是'0000-00-00'，而NO_ZERO_IN_DATE针对的是年不为0，但月或者日为0的日期，如，'2010-00-01' or '2010-01-00'。

实际结果也是取决于可否开启严厉模式，同NO_ZERO_DATE一样。

ONLY_FULL_GROUP_BY

开启该MODE，则SELECT列表中只能显现分组列和聚合函数。

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

mysql> select dept_no,emp_no,min(from_date) from dept_emp group by dept_no;
+---------+--------+----------------+
| dept_no | emp_no | min(from_date) |
+---------+--------+----------------+
| d001    |  10017 | 1985-01-01     |
| d002    |  10042 | 1985-01-01     |
| d003    |  10005 | 1985-01-01     |
| d004    |  10003 | 1985-01-01     |
| d005    |  10001 | 1985-01-01     |
| d006    |  10009 | 1985-01-01     |
| d007    |  10002 | 1985-01-01     |
| d008    |  10007 | 1985-01-01     |
| d009    |  10011 | 1985-01-01     |
+---------+--------+----------------+
rows in set (0.64 sec)

mysql> set session sql_mode='ONLY_FULL_GROUP_BY';
Query OK, 0 rows affected (0.00 sec)

mysql> select dept_no,emp_no,min(from_date) from dept_emp group by dept_no;
ERROR 1055 (42000): Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'employees.dept_emp.emp_no' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

假如不开启该MODE，则同意SELECT列表中显现任意列，但这些列的值并不是肯定的，官方文档中也提到了这一点。

If ONLY_FULL_GROUP_BY is disabled, a MySQL extension to the standard SQL use of GROUP BY permits the select list, HAVING condition, or ORDER BY list to refer to nonaggregated columns even if the columns are not functionally dependent on GROUP BY columns. This causes MySQL to accept the preceding query. 

In this case, the server is free to choose any value from each group, so unless they are the same, the values chosen are nondeterministic, which is probably not what you want. 

Furthermore, the selection of values from each group cannot be influenced by adding an ORDER BY clause. Result set sorting occurs after values have been chosen, and ORDER BY does not affect which value within each group the server chooses. 

Disabling ONLY_FULL_GROUP_BY is useful primarily when you know that, due to some property of the data, all values in each nonaggregated column not named in the GROUP BY are the same for each group.

https://dev.mysql.com/doc/refman/8.0/en/group-by-handling.html

PAD_CHAR_TO_FULL_LENGTH

在对CHAR字段停止储备时，在Compact格局下，会占用牢固长度的字节。

如下面的c1列，定义为char(10)，虽然'ab'只占用两个字节，但在Compact格局下，会占用10个字节，不足部分以空格填充。

在查询时，默许状况下，会剔除掉末尾的空格。若开启该MODE，则不会剔除，每次都会返回牢固长度的字符。

mysql> create table t (c1 char(10));
Query OK, 0 rows affected (0.17 sec)

mysql> insert into t values('ab');
Query OK, 1 row affected (0.11 sec)

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

mysql> select c1, hex(c1), char_length(c1) from t;
+------+---------+-----------------+
| c1   | hex(c1) | char_length(c1) |
+------+---------+-----------------+
| ab   | 6162    |               2 |
+------+---------+-----------------+
row in set (0.00 sec)

mysql> set session sql_mode='PAD_CHAR_TO_FULL_LENGTH';
Query OK, 0 rows affected (0.00 sec)

mysql> select c1, hex(c1), char_length(c1) from t;
+------------+----------------------+-----------------+
| c1         | hex(c1)              | char_length(c1) |
+------------+----------------------+-----------------+
| ab         | 61622020202020202020 |              10 |
+------------+----------------------+-----------------+
row in set (0.00 sec)

PIPES_AS_CONCAT

在Oracle中，连接字符串可用concat和管道符（"||"），但concat只能连接两个字符串（MySQL中的concat可连接多个字符），局限性太大，假如要连接多个字符串，一样用的是管道符。

开启该MODE，即可将管道符作为连接符。

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

mysql> select 'a'||'b';
+----------+
| 'a'||'b' |
+----------+
|        0 |
+----------+
row in set, 2 warnings (0.00 sec)

mysql> select concat('a','b');
+-----------------+
| concat('a','b') |
+-----------------+
| ab              |
+-----------------+
row in set (0.00 sec)

mysql> set session sql_mode='PIPES_AS_CONCAT';
Query OK, 0 rows affected (0.00 sec)

mysql> select 'a'||'b';
+----------+
| 'a'||'b' |
+----------+
| ab       |
+----------+
row in set (0.00 sec)

REAL_AS_FLOAT

在创立表时，数据类型可指定为real，默许状况下，其会转化为double，若开启该MODE，则会转化为float。

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

mysql> create table t ( c1 real);
Query OK, 0 rows affected (0.12 sec)

mysql> show create table t\G
*************************** 1. row ***************************
       Table: t
Create Table: CREATE TABLE `t` (
  `c1` double DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
row in set (0.00 sec)

mysql> drop table t;
Query OK, 0 rows affected (0.04 sec)

mysql> set session sql_mode='REAL_AS_FLOAT';
Query OK, 0 rows affected (0.00 sec)

mysql> create table t ( c1 real);
Query OK, 0 rows affected (0.11 sec)

mysql> show create table t\G
*************************** 1. row ***************************
       Table: t
Create Table: CREATE TABLE `t` (
  `c1` float DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
row in set (0.00 sec)

STRICT_ALL_TABLES

对事务表开启严厉模式。

STRICT_TRANS_TABLES

对所有表开启严厉模式。

TIME_TRUNCATE_FRACTIONAL

在时间类型定义了小数秒的状况下，假如插入的位数大于指定的位数，默许状况下，会四舍五入，若开启了该MODE，则会直接truncate掉。

mysql> create table t (c1 int,c2 datetime(2));
Query OK, 0 rows affected (0.04 sec)

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

mysql> insert into t values(1,'2018-08-08 11:12:13.125');
Query OK, 1 row affected (0.06 sec)

mysql> select * from t;
+------+------------------------+
| c1   | c2                     |
+------+------------------------+
|    1 | 2018-08-08 11:12:13.13 |
+------+------------------------+
row in set (0.00 sec)

mysql> set session sql_mode='TIME_TRUNCATE_FRACTIONAL';
Query OK, 0 rows affected (0.00 sec)

mysql> insert into t values(2,'2018-08-08 11:12:13.125');
Query OK, 1 row affected (0.06 sec)

mysql> select * from t;
+------+------------------------+
| c1   | c2                     |
+------+------------------------+
|    1 | 2018-08-08 11:12:13.13 |
|    2 | 2018-08-08 11:12:13.12 |
+------+------------------------+
rows in set (0.00 sec)

NO_AUTO_CREATE_USER

在MySQL 8.0此前，直接授权会隐式创立会员。

mysql> select host,user from mysql.user where user='u1';
Empty set (0.00 sec)

mysql> grant all on *.* to 'u1'@'%' identified by '123';
Query OK, 0 rows affected, 1 warning (0.12 sec)

mysql> show warnings;
+---------+------+------------------------------------------------------------------------------------------------------------------------------------+
| Level   | Code | Message                                                                                                                            |
+---------+------+------------------------------------------------------------------------------------------------------------------------------------+
| Warning | 1287 | Using GRANT for creating new user is deprecated and will be removed in future release. Create new user with CREATE USER statement. |
+---------+------+------------------------------------------------------------------------------------------------------------------------------------+
row in set (0.00 sec)

mysql> select host,user from mysql.user where user='u1';
+------+------+
| host | user |
+------+------+
| %    | u1   |
+------+------+
row in set (0.00 sec)

一样的grant语句，在MySQL 8.0中是会报错的。

mysql> grant all on *.* to 'u1'@'%' identified by '123';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'identified by '123'' at line 1

在MySQL 8.0中，已不同意grant语句隐式创立会员，所以，该MODE在8.0中也不存在。

从字面上看，该MODE是制止授权时隐式创立会员。但在实际测试历程中，发明其并不克不及制止。

mysql> set session sql_mode='NO_AUTO_CREATE_USER';
Query OK, 0 rows affected (0.03 sec)

mysql> grant all on *.* to 'u1'@'%' identified by '123';
Query OK, 0 rows affected, 1 warning (0.00 sec)

其实，该MODE制止的只是不带“identified by”子句的grant语句，关于带有“identified by”子句的grant语句，其并不会制止。

mysql> drop user u1;
Query OK, 0 rows affected (0.00 sec)

mysql> set session sql_mode='NO_AUTO_CREATE_USER';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> grant all on *.* to 'u1'@'%';
ERROR 1133 (42000): Can't find any matching row in the user table

mysql> set session sql_mode='';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> grant all on *.* to 'u1'@'%';
Query OK, 0 rows affected, 1 warning (0.00 sec)

SQL_MODE的常见组合

在MySQL 5.7中，还可将SQL_MODE设定为ANSI, DB2, MAXDB, MSSQL, MYSQL323, MYSQL40, ORACLE, POSTGRESQL, TRADITIONAL。

其实，这些MODE只是上述MODE的一种组合，目的是为了和其它数据库兼容。

在MySQL 8.0中，只支撑ANSI和TRADITIONAL这两种组合。

ANSI

等同于REAL_AS_FLOAT, PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, ONLY_FULL_GROUP_BY。

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

mysql> show session variables like 'sql_mode';
+---------------+--------------------------------------------------------------------------------+
| Variable_name | Value                                                                          |
+---------------+--------------------------------------------------------------------------------+
| sql_mode      | REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ONLY_FULL_GROUP_BY,ANSI |
+---------------+--------------------------------------------------------------------------------+
row in set (0.03 sec)

TRADITIONAL

等同于STRICT_TRANS_TABLES, STRICT_ALL_TABLES, NO_ZERO_IN_DATE, NO_ZERO_DATE, ERROR_FOR_pISION_BY_ZERO, NO_ENGINE_SUBSTITUTION。

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

mysql> show session variables like 'sql_mode';
+---------------+----------------------------------------------------------------------------------------------------------------------------------+
| Variable_name | Value                                                                                                                            |
+---------------+----------------------------------------------------------------------------------------------------------------------------------+
| sql_mode      | STRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,TRADITIONAL,NO_ENGINE_SUBSTITUTION |
+---------------+----------------------------------------------------------------------------------------------------------------------------------+
row in set (0.01 sec)

总结

1. SQL_MODE在非严厉模式下，会显现许多料想不到的结果。倡议线上开启严厉模式。但关于线上老的环境，假如一开端就运转在非严厉模式下，切忌直接调整，究竟两者的差别性还是相当宏大。

2. 官方默许的SQL_MODE不断在发生转变，MySQL 5.5, 5.6, 5.7就不尽雷同，但总体是趋严的，在对数据库停止升级时，其必需思考默许的SQL_MODE可否需要调整。

3. 在停止数据库迁移时，可通过调整SQL_MODE来兼容其它数据库的语法。

引荐学习：MySQL教程

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