采坑之运用MySQL，SQL_MODE有哪些坑【MySQL教程】,MySQL,SQL_MODE

SQL_MODE是MySQL中的一个体系变量（variable），可由多个MODE构成，每一个MODE掌握一种行动，如是不是许可除数为0，日期中是不是许可'0000-00-00'值。

为何须要关注SQL_MODE呢？

起首，看三个简朴的Demo（MySQL 5.6）。

1.

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)

现实存储值与插进去值不符。

2.

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。

3.

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惩罚逻辑居然不一样。

为何会如许呢？这个即与SQL_MODE有关。

在MySQL 5.6中， SQL_MODE的默许值为"NO_ENGINE_SUBSTITUTION"，非严厉形式。

在这类形式下，在举行数据变动操纵时，假如触及的列中存在无效值（如日期不存在，数据范例不对，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的严厉形式。

SQL_MODE的严厉形式

所谓的严厉形式，即SQL_MODE中开启了STRICT_ALL_TABLES或STRICT_TRANS_TAB LES。

照样上面的Demo，看看严厉形式下，MySQL的处置惩罚逻辑。

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，在严厉形式下，直接提醒"ERROR"，而不是"Warning"。

同是严厉形式，下面看看STRICT_ALL_TABLES或STRICT_TRAN S_TABLES的区分。

STRICT_ALL_TABLES与STRICT_TRANS_TABLES的区分

STRICT_TRANS_TABLES只对事件表开启严厉形式，STRICT_ALL_TABLES是对一切表开启严厉形式，不仅仅是事件表，还包含非事件表。

看下面这个测试。

对myisam表插进去3条数据，个中，第3条数据是空字符串，与定义的int范例不婚配。

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

能够看到，在表为myisam存储引擎的状况下，只要开启STRICT_ALL_TABLES才会报错。

差别版本默许的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

怎样修正SQL_MODE

SQL_MODE既可在全局级别修正，又可在会话级别修正。可指定多个MODE，MODE之间用逗号离隔。

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

在严厉形式下，关于日期的检测较为严厉，其必需有用。若开启该MODE，关于month和day的检测会相对宽松。个中，month只需在1~12之间，day只需在1~31之间，而不论其是不是有用，以下面的'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)

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

ANSI_QUOTES

在MySQL中，关于关键字和保留字，是不许可用做表名和字段名的。假如一定要运用，必需运用反引号（"`"）举行转义。

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，可对关键字和保留字转义。

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)

须要注重的是，在开启该MODE的状况下，不能再用双引号来引字符串。

ERROR_FOR_pISION_BY_ZERO

该MODE决议除数为0的处置惩罚逻辑，现实效果还取决于是不是开启严厉形式。

1. 开启严厉形式，且开启该MODE，插进去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. 只开启严厉形式，不开启该MODE，许可1/0的插进去，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. 不开启严厉形式，只开启该MODE，许可1/0的插进去，但提醒warning。

4. 不开启严厉形式，也不开启该MODE，许可1/0的插进去，且不提醒warning，同2一样。

HIGH_NOT_PRECEDENCE

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

看看二者的区分。

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相称于not (1 < -1)，假如设置了'HIGH_ NOT_PRECEDENCE'，则相称于(not 1) < -1。

IGNORE_SPACE

默许状况下，函数名和左括号（“(”）之间不许可存在空格。若开启该MODE，则许可。

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，在对自增主键插进去NULL或0时，会自动生成下一个值。若开启该MODE，当插进去0时，并不会自动生成下一个值。

假如表中自增主键列存在0值，在举行逻辑备份复原时，可能会致使数据不一致。所以mysqldump在生成备份数据之前，会自动开启该MODE，以防止数据不一致的状况。

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，反斜杠“\”会作为转义符，若开启该MODE，则反斜杠“\”会作为一个平常字符，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，在建立表时，能够指定数据目次（DATA DIRECTORY）和索引目次（INDEX DIRECTORY），若开启该MODE，则会疏忽这两个选项。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，在建立表时，假如指定的存储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”，且运用默许的存储引擎。

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，假如个中一个数是无标记位，默许状况下，会发生一个无标记位的值，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，则许可效果为负数。

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'的插进去。现实效果还取决于是不是开启严厉形式。

1. 在开启严厉形式，且同时开启该MODE，是不许可'0000-00-00'插进去的。

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. 只开启严厉形式，不开启该MODE，许可'0000-00-00'值的插进去，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. 不开启严厉形式，只开启该MODE，许可'0000-00-00'值的插进去，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. 不开启严厉形式，也不开启该MODE，许可'0000-00-00'值的插进去，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，只不过NO_ZERO_DATE针对的是'0000-00-00'，而NO_ZERO_IN_DATE针对的是年不为0，但月或许日为0的日期，如，'2010-00-01' or '2010-01-00'。

现实效果也是取决于是不是开启严厉形式，同NO_ZERO_DATE一样。

ONLY_FULL_GROUP_BY

开启该MODE，则SELECT列表中只能涌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，则许可SELECT列表中涌现恣意列，但这些列的值并非肯定的，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字段举行存储时，在Compact花样下，会占用牢固长度的字节。

以下面的c1列，定义为char(10)，虽然'ab'只占用两个字节，但在Compact花样下，会占用10个字节，不足部份以空格添补。

在查询时，默许状况下，会剔撤除末端的空格。若开启该MODE，则不会剔除，每次都邑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，衔接字符串可用concat和管道符（"||"），但concat只能衔接两个字符串（MySQL中的concat可衔接多个字符），局限性太大，假如要衔接多个字符串，平常用的是管道符。

开启该MODE，即可将管道符作为衔接符。

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

在建立表时，数据范例可指定为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

对事件表开启严厉形式。

STRICT_TRANS_TABLES

对一切表开启严厉形式。

TIME_TRUNCATE_FRACTIONAL

在时候范例定义了小数秒的状况下，假如插进去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之前，直接受权会隐式建立用户。

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，已不许可grant语句隐式建立用户，所以，该MODE在8.0中也不存在。

从字面上看，该MODE是制止受权时隐式建立用户。但在现实测试过程当中，发明其并不能制止。

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)

实在，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的罕见组合

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

实在，这些MODE只是上述MODE的一种组合，目标是为了和别的数据库兼容。

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在非严厉形式下，会涌现许多意料不到的效果。发起线上开启严厉形式。但关于线上老的环境，假如一开始就运行在非严厉形式下，切忌直接调解，毕竟二者的差异性照样相称庞大。

2. 官方默许的SQL_MODE一直在发生变化，MySQL 5.5, 5.6, 5.7就不尽相同，但整体是趋严的，在对数据库举行升级时，其必需斟酌默许的SQL_MODE是不是须要调解。

3. 在举行数据库迁移时，可通过调解SQL_MODE来兼容别的数据库的语法。

引荐进修：MySQL教程

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