mysql数据类型和常用函数

1.整型

1.1参数signed和unsigned

1.2参数zerofill

1.3参数auto_increment

2.数字类型

2.1floor()向下取整

2.2随机函数rand()

2.3重复函数repeat()

3.字符串类型

3.1length()查看字节长度，char_length()查看字符长度

3.2字符集

3.2.1查看默认字符集

3.2.2查看已经创建的数据库的字符集

3.2.3修改已经创建的数据库的字符集

3.2.4修改mysql默认字符集

3.2.5两条转换表字符集的语句

3.2.6查看支持的字符集

3.3hex()函数

3.4cast()函数

3.5排序规则collation

3.6对于密码的加密，md5()函数

3.7upper()和lower()函数

3.8concat()和concat_ws()函数

3.9lpad()和rpad()函数

4.enum&set类型

5.时间类型

5.1日期函数

编辑 5.1.1now()函数

5.1.2now()和sysdate()的区别

5.1.3date_add()和date_sub()函数

5.1.4date_format()函数

6.json类型

6.1json类型相关函数

6.1.1json_extract()函数

6.1.2json_remove()函数

mysql的数据类型有：整型、数字类型、字符串类型、日期类型、json类型等主要类型

1.整型

1.1参数signed和unsigned

可以创建有符号(signed)和无符号(unsigned)的整型类型

(root@localhost) [(none)]> use python;
Database changed
(root@localhost) [python]> create table z (a int unsigned,b tinyint signed);
Query OK, 0 rows affected (0.58 sec)(root@localhost) [python]> insert into z values(1,1);
Query OK, 1 row affected (0.13 sec)(root@localhost) [python]> insert into z values(-1,1);
ERROR 1264 (22003): Out of range value for column 'a' at row 1
(root@localhost) [python]> insert into z values(1,-1);
Query OK, 1 row affected (0.05 sec)(root@localhost) [python]> select * from z;
+------+------+
| a    | b    |
+------+------+
|    1 |    1 |
|    1 |   -1 |
+------+------+
2 rows in set (0.00 sec)

1.2参数zerofill

查看创建表ddl有int(10)和tinyint(4)，其中10和4代表显示的数值总长度，长度不够用0填充

(root@localhost) [python]> show create table z\G
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` int(10) unsigned DEFAULT NULL,`b` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.04 sec)(root@localhost) [python]> alter table z change column a a int unsigned zerofill;
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0(root@localhost) [python]> select * from z;
+------------+------+
| a          | b    |
+------------+------+
| 0000000001 |    1 |
| 0000000001 |   -1 |
+------------+------+
2 rows in set (0.00 sec)(root@localhost) [python]> show create table z\G
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` int(10) unsigned zerofill DEFAULT NULL,`b` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

可以修改显示的总长度

(root@localhost) [python]> alter table z change column a a int(4) unsigned zerofill;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0(root@localhost) [python]> select * from z;
+------+------+
| a    | b    |
+------+------+
| 0001 |    1 |
| 0001 |   -1 |
+------+------+
2 rows in set (0.00 sec)(root@localhost) [python]> show create table z\G
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` int(4) unsigned zerofill DEFAULT NULL,`b` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

可以正常插入比显示长度更大的值

(root@localhost) [python]> insert into z values(20000,2);
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> select * from z;
+-------+------+
| a     | b    |
+-------+------+
|  0001 |    1 |
|  0001 |   -1 |
| 20000 |    2 |
+-------+------+
3 rows in set (0.00 sec)

1.3参数auto_increment

设置该参数，主键自动递增，select last_insert_id()查询上一次自增id值是多少，表数据量大主键自增字段建议用bigint类型

(root@localhost) [python]> truncate table z;
Query OK, 0 rows affected (0.13 sec)(root@localhost) [python]> alter table z change column a a int auto_increment primary key;
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0(root@localhost) [python]> show create table z\G
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` int(11) NOT NULL AUTO_INCREMENT,`b` tinyint(4) DEFAULT NULL,PRIMARY KEY (`a`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)(root@localhost) [python]> insert into z values(null,10);
Query OK, 1 row affected (0.01 sec)(root@localhost) [python]> insert into z values(null,20);
Query OK, 1 row affected (0.01 sec)(root@localhost) [python]> insert into z(b) values(30);
Query OK, 1 row affected (0.05 sec)(root@localhost) [python]> insert into z values(40);
ERROR 1136 (21S01): Column count doesn't match value count at row 1
(root@localhost) [python]> select * from z;
+---+------+
| a | b    |
+---+------+
| 1 |   10 |
| 2 |   20 |
| 3 |   30 |
+---+------+
3 rows in set (0.00 sec)(root@localhost) [python]> select last_insert_id();
+------------------+
| last_insert_id() |
+------------------+
|                3 |
+------------------+
1 row in set (0.06 sec)

自增字段值在不重启数据库的情况下不会回溯，只会越来越大

(root@localhost) [python]> delete from z where b=30;
Query OK, 1 row affected (0.06 sec)(root@localhost) [python]> insert into z values(null,30);
Query OK, 1 row affected (0.04 sec)(root@localhost) [python]> select * from z;
+---+------+
| a | b    |
+---+------+
| 1 |   10 |
| 2 |   20 |
| 4 |   30 |
+---+------+
3 rows in set (0.00 sec)

自增字段在删除select last_insert_id()的值后，重启数据库会回溯，查看ddl，AUTO_INCREMENT=7

(root@localhost) [python]> select * from z;
+---+------+
| a | b    |
+---+------+
| 1 |   10 |
| 2 |   20 |
| 5 |   40 |
| 6 |   30 |
+---+------+
4 rows in set (0.00 sec)(root@localhost) [python]> show create table z\G
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` int(11) NOT NULL AUTO_INCREMENT,`b` tinyint(4) DEFAULT NULL,PRIMARY KEY (`a`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)(root@localhost) [python]> delete from z where a=6;
Query OK, 1 row affected (0.01 sec)(root@localhost) [python]> delete from z where a=5;
Query OK, 1 row affected (0.01 sec)(root@localhost) [python]> select * from z;
+---+------+
| a | b    |
+---+------+
| 1 |   10 |
| 2 |   20 |
+---+------+
2 rows in set (0.00 sec)

删除a=6、a=5后重启数据库查看ddl，AUTO_INCREMENT=3，此时就回溯了，再次插入数据a=3、a=4就回来了，线上删除的值就又出现了，会乱掉，这个问题在mysql8.0得到解决

(root@localhost) [python]> show create table z\G
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` int(11) NOT NULL AUTO_INCREMENT,`b` tinyint(4) DEFAULT NULL,PRIMARY KEY (`a`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)(root@localhost) [python]> select * from z;
+---+------+
| a | b    |
+---+------+
| 1 |   10 |
| 2 |   20 |
+---+------+
2 rows in set (0.00 sec)(root@localhost) [python]> insert into z values(null,30);
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> insert into z values(null,40);
Query OK, 1 row affected (0.01 sec)(root@localhost) [python]> select * from z;
+---+------+
| a | b    |
+---+------+
| 1 |   10 |
| 2 |   20 |
| 3 |   30 |
| 4 |   40 |
+---+------+
4 rows in set (0.00 sec)(root@localhost) [python]>

mysql8.0解决自增字段回溯问题，AUTO_INCREMENT值持久化

[root@localhost ~]# mysql -S/tmp/mysql.sock80 -uroot -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 19
Server version: 8.0.35 MySQL Community Server - GPLCopyright (c) 2000, 2023, Oracle and/or its affiliates.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.(root@localhost) [(none)]> create database zs;
Query OK, 1 row affected (0.42 sec)(root@localhost) [(none)]> use zs
Database changed
(root@localhost) [zs]> create table z (a bigint auto_increment primary key,b tinyint);
Query OK, 0 rows affected (1.36 sec)(root@localhost) [zs]> show create table z\G;
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` bigint NOT NULL AUTO_INCREMENT,`b` tinyint DEFAULT NULL,PRIMARY KEY (`a`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.22 sec)ERROR: 
No query specified(root@localhost) [zs]> insert into z values(null,10);
Query OK, 1 row affected (0.08 sec)(root@localhost) [zs]> insert into z values(null,20);
Query OK, 1 row affected (0.05 sec)(root@localhost) [zs]> insert into z values(null,30);
Query OK, 1 row affected (0.05 sec)(root@localhost) [zs]> insert into z values(null,40);
Query OK, 1 row affected (0.01 sec)(root@localhost) [zs]> show create table z\G;
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` bigint NOT NULL AUTO_INCREMENT,`b` tinyint DEFAULT NULL,PRIMARY KEY (`a`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)ERROR: 
No query specified(root@localhost) [zs]> select * from z;
+---+------+
| a | b    |
+---+------+
| 1 |   10 |
| 2 |   20 |
| 3 |   30 |
| 4 |   40 |
+---+------+
4 rows in set (0.01 sec)(root@localhost) [zs]> delete from z where a=4;
Query OK, 1 row affected (0.06 sec)(root@localhost) [zs]> delete from z where a=3;
Query OK, 1 row affected (0.05 sec)(root@localhost) [zs]> select * from z;
+---+------+
| a | b    |
+---+------+
| 1 |   10 |
| 2 |   20 |
+---+------+
2 rows in set (0.00 sec)(root@localhost) [zs]> show create table z\G;
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` bigint NOT NULL AUTO_INCREMENT,`b` tinyint DEFAULT NULL,PRIMARY KEY (`a`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)ERROR: 
No query specified(root@localhost) [zs]> exit
Bye
[root@localhost ~]# mysqld_multi stop 80
[root@localhost ~]# mysqld_multi report
Reporting MySQL servers
MySQL server from group: mysqld32 is not running
MySQL server from group: mysqld1 is not running
MySQL server from group: mysqld2 is not running
MySQL server from group: mysqld80 is not running
[root@localhost ~]# mysqld_multi start 80
[root@localhost ~]# mysqld_multi report
Reporting MySQL servers
MySQL server from group: mysqld32 is not running
MySQL server from group: mysqld1 is not running
MySQL server from group: mysqld2 is not running
MySQL server from group: mysqld80 is running
[root@localhost ~]# mysql -S/tmp/mysql.sock80 -uroot -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 9
Server version: 8.0.35 MySQL Community Server - GPLCopyright (c) 2000, 2023, Oracle and/or its affiliates.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.(root@localhost) [(none)]> use zs;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -ADatabase changed
(root@localhost) [zs]> show create table z\G;
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` bigint NOT NULL AUTO_INCREMENT,`b` tinyint DEFAULT NULL,PRIMARY KEY (`a`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)ERROR: 
No query specified(root@localhost) [zs]> select * from z;
+---+------+
| a | b    |
+---+------+
| 1 |   10 |
| 2 |   20 |
+---+------+
2 rows in set (0.00 sec)(root@localhost) [zs]> insert into z values(null,30);
Query OK, 1 row affected (0.01 sec)(root@localhost) [zs]> insert into z values(null,40);
Query OK, 1 row affected (0.00 sec)(root@localhost) [zs]> select * from z;
+---+------+
| a | b    |
+---+------+
| 1 |   10 |
| 2 |   20 |
| 5 |   30 |
| 6 |   40 |
+---+------+
4 rows in set (0.00 sec)(root@localhost) [zs]>

int类型总结

推荐不要使用UNSIGNED
范围本质上没有大的改变
UNSIGNED可能会有溢出现象发生
自增INT类型主键建议使用BIGINT

2.数字类型

一般建议用decimal

2.1floor()向下取整

(root@localhost) [(none)]> select floor(1.5);
+------------+
| floor(1.5) |
+------------+
|          1 |
+------------+
1 row in set (0.00 sec)(root@localhost) [(none)]> select floor(1.9);
+------------+
| floor(1.9) |
+------------+
|          1 |
+------------+
1 row in set (0.00 sec)(root@localhost) [(none)]> select floor(-1.9);
+-------------+
| floor(-1.9) |
+-------------+
|          -2 |
+-------------+
1 row in set (0.00 sec)

2.2随机函数rand()

(root@localhost) [(none)]> select rand() ;
+-------------------+
| rand()            |
+-------------------+
| 0.590530601880076 |
+-------------------+
1 row in set (0.00 sec)(root@localhost) [(none)]> select rand() ;
+--------------------+
| rand()             |
+--------------------+
| 0.1034116913596277 |
+--------------------+
1 row in set (0.00 sec)

1~100随机整数

(root@localhost) [(none)]> select floor(1+rand()*99);
+--------------------+
| floor(1+rand()*99) |
+--------------------+
|                 74 |
+--------------------+
1 row in set (0.00 sec)(root@localhost) [(none)]> select floor(1+rand()*99);
+--------------------+
| floor(1+rand()*99) |
+--------------------+
|                 42 |
+--------------------+
1 row in set (0.00 sec)(root@localhost) [(none)]> select floor(1+rand()*99);
+--------------------+
| floor(1+rand()*99) |
+--------------------+
|                 85 |
+--------------------+
1 row in set (0.00 sec)

2.3重复函数repeat()

(root@localhost) [(none)]> select repeat(1,3);
+-------------+
| repeat(1,3) |
+-------------+
| 111         |
+-------------+
1 row in set (0.00 sec)(root@localhost) [(none)]> select repeat(32,3);
+--------------+
| repeat(32,3) |
+--------------+
| 323232       |
+--------------+
1 row in set (0.00 sec)(root@localhost) [(none)]> select repeat('b',5);
+---------------+
| repeat('b',5) |
+---------------+
| bbbbb         |
+---------------+
1 row in set (0.00 sec)(root@localhost) [(none)]> select repeat('ba',4);
+----------------+
| repeat('ba',4) |
+----------------+
| babababa       |
+----------------+
1 row in set (0.00 sec)

字符串或数字变长

(root@localhost) [mysql]> select repeat('a',floor(1+rand()*99));
+-----------------------------------------------------------------------------------------------------+
| repeat('a',floor(1+rand()*99))                                                                      |
+-----------------------------------------------------------------------------------------------------+
| aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |
+-----------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)(root@localhost) [mysql]> select repeat('a',floor(1+rand()*99));
+--------------------------------------------+
| repeat('a',floor(1+rand()*99))             |
+--------------------------------------------+
| aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |
+--------------------------------------------+
1 row in set (0.00 sec)(root@localhost) [mysql]> select repeat('b1',floor(1+rand()*20));
+---------------------------------+
| repeat('b1',floor(1+rand()*20)) |
+---------------------------------+
| b1b1b1                          |
+---------------------------------+
1 row in set (0.00 sec)(root@localhost) [mysql]> select repeat('b1',floor(1+rand()*20));
+---------------------------------+
| repeat('b1',floor(1+rand()*20)) |
+---------------------------------+
| b1b1b1b1b1b1b1b1b1              |
+---------------------------------+
1 row in set (0.00 sec)

3.字符串类型

char(n)和varchar(n)中的n代表字符，有字符集

(root@localhost) [python]> drop table z;
Query OK, 0 rows affected (0.72 sec)(root@localhost) [python]> create table z (a char(1),b varchar(3),c binary(1),d varbinary(3));
Query OK, 0 rows affected (0.02 sec)(root@localhost) [python]> insert into z values('a','bbb','c','ddd');
Query OK, 1 row affected (0.01 sec)(root@localhost) [python]> select * from z;
+------+------+------+------+
| a    | b    | c    | d    |
+------+------+------+------+
| a    | bbb  | c    | ddd  |
+------+------+------+------+
1 row in set (0.00 sec)(root@localhost) [python]> show create table z\G
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` char(1) DEFAULT NULL,`b` varchar(3) DEFAULT NULL,`c` binary(1) DEFAULT NULL,`d` varbinary(3) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)(root@localhost) [python]> insert into z values('紫','bbc','x','ooo');
ERROR 1366 (HY000): Incorrect string value: '\xE7\xB4\xAB' for column 'a' at row 1
(root@localhost) [python]> alter table z convert to charset utf8mb4;
Query OK, 1 row affected (0.04 sec)
Records: 1  Duplicates: 0  Warnings: 0(root@localhost) [python]> show create table z\G
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` char(1) DEFAULT NULL,`b` varchar(3) DEFAULT NULL,`c` binary(1) DEFAULT NULL,`d` varbinary(3) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
1 row in set (0.00 sec)(root@localhost) [python]> insert into z values('紫','bbc','x','ooo');
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> insert into z values('x','bbc','紫','ooo');
ERROR 1406 (22001): Data too long for column 'c' at row 1

3.1length()查看字节长度，char_length()查看字符长度

(root@localhost) [python]> select length('紫'),char_length('紫');
+---------------+--------------------+
| length('紫')  | char_length('紫')  |
+---------------+--------------------+
|             3 |                  1 |
+---------------+--------------------+
1 row in set (0.00 sec)

3.2字符集

mysql中的字符集最小是在列级别上

3.2.1查看默认字符集

(root@localhost) [python]> show variables like '%character%';
+--------------------------+----------------------------------------------------------------+
| Variable_name            | Value                                                          |
+--------------------------+----------------------------------------------------------------+
| character_set_client     | utf8                                                           |
| character_set_connection | utf8                                                           |
| character_set_database   | latin1                                                         |
| character_set_filesystem | binary                                                         |
| character_set_results    | utf8                                                           |
| character_set_server     | utf8mb4                                                        |
| character_set_system     | utf8                                                           |
| character_sets_dir       | /usr/local/mysql-5.7.44-linux-glibc2.12-x86_64/share/charsets/ |
+--------------------------+----------------------------------------------------------------+

3.2.2查看已经创建的数据库的字符集

(root@localhost) [zs]> show create database python;
+----------+-------------------------------------------------------------------+
| Database | Create Database                                                   |
+----------+-------------------------------------------------------------------+
| python   | CREATE DATABASE `python` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+----------+-------------------------------------------------------------------+
1 row in set (0.00 sec)

3.2.3修改已经创建的数据库的字符集

(root@localhost) [python]> alter database python charset utf8mb4;
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> show create database python;
+----------+--------------------------------------------------------------------+
| Database | Create Database                                                    |
+----------+--------------------------------------------------------------------+
| python   | CREATE DATABASE `python` /*!40100 DEFAULT CHARACTER SET utf8mb4 */ |
+----------+--------------------------------------------------------------------+
1 row in set (0.00 sec)

3.2.4修改mysql默认字符集

在my.cnf中加入参数

[mysqld]

character_set_server=utf8mb4

3.2.5两条转换表字符集的语句

alter table t charset utf8mb4;与alter table t convert to charset(或者character set) utf8mb4;的不同，前者对已经存在的列不进行字符集转换，只对新增列转换，后者是对已经存在的列和新增列都转换，旧的字符集是新的字符集的子集，在生产上要注意转换字符集是要锁表的，要小心

(root@localhost) [python]> drop table t;
Query OK, 0 rows affected (0.01 sec)(root@localhost) [python]> create table t(a varchar(10),b char(2)) charset gbk;
Query OK, 0 rows affected (0.04 sec)(root@localhost) [python]> show create table t\G;
*************************** 1. row ***************************Table: t
Create Table: CREATE TABLE `t` (`a` varchar(10) DEFAULT NULL,`b` char(2) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=gbk
1 row in set (0.00 sec)ERROR: 
No query specified(root@localhost) [python]> alter table t charset utf8mb4;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0(root@localhost) [python]> show create table t\G;
*************************** 1. row ***************************Table: t
Create Table: CREATE TABLE `t` (`a` varchar(10) CHARACTER SET gbk DEFAULT NULL,`b` char(2) CHARACTER SET gbk DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
1 row in set (0.00 sec)ERROR: 
No query specified(root@localhost) [python]> alter table t add column c varchar(11);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0(root@localhost) [python]> show create table t\G;
*************************** 1. row ***************************Table: t
Create Table: CREATE TABLE `t` (`a` varchar(10) CHARACTER SET gbk DEFAULT NULL,`b` char(2) CHARACTER SET gbk DEFAULT NULL,`c` varchar(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
1 row in set (0.00 sec)ERROR: 
No query specified(root@localhost) [python]> alter table t convert to charset utf8mb4;
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0(root@localhost) [python]> show create table t\G;
*************************** 1. row ***************************Table: t
Create Table: CREATE TABLE `t` (`a` varchar(10) DEFAULT NULL,`b` char(2) DEFAULT NULL,`c` varchar(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
1 row in set (0.00 sec)ERROR: 
No query specified

3.2.6查看支持的字符集

show charset，Maxlen表示最大的一个字符占用多少个字节

(root@localhost) [python]> show charset;
+----------+---------------------------------+---------------------+--------+
| Charset  | Description                     | Default collation   | Maxlen |
+----------+---------------------------------+---------------------+--------+
| big5     | Big5 Traditional Chinese        | big5_chinese_ci     |      2 |
| dec8     | DEC West European               | dec8_swedish_ci     |      1 |
| cp850    | DOS West European               | cp850_general_ci    |      1 |
| hp8      | HP West European                | hp8_english_ci      |      1 |
| koi8r    | KOI8-R Relcom Russian           | koi8r_general_ci    |      1 |
| latin1   | cp1252 West European            | latin1_swedish_ci   |      1 |
| latin2   | ISO 8859-2 Central European     | latin2_general_ci   |      1 |
| swe7     | 7bit Swedish                    | swe7_swedish_ci     |      1 |
| ascii    | US ASCII                        | ascii_general_ci    |      1 |
| ujis     | EUC-JP Japanese                 | ujis_japanese_ci    |      3 |
| sjis     | Shift-JIS Japanese              | sjis_japanese_ci    |      2 |
| hebrew   | ISO 8859-8 Hebrew               | hebrew_general_ci   |      1 |
| tis620   | TIS620 Thai                     | tis620_thai_ci      |      1 |
| euckr    | EUC-KR Korean                   | euckr_korean_ci     |      2 |
| koi8u    | KOI8-U Ukrainian                | koi8u_general_ci    |      1 |
| gb2312   | GB2312 Simplified Chinese       | gb2312_chinese_ci   |      2 |
| greek    | ISO 8859-7 Greek                | greek_general_ci    |      1 |
| cp1250   | Windows Central European        | cp1250_general_ci   |      1 |
| gbk      | GBK Simplified Chinese          | gbk_chinese_ci      |      2 |
| latin5   | ISO 8859-9 Turkish              | latin5_turkish_ci   |      1 |
| armscii8 | ARMSCII-8 Armenian              | armscii8_general_ci |      1 |
| utf8     | UTF-8 Unicode                   | utf8_general_ci     |      3 |
| ucs2     | UCS-2 Unicode                   | ucs2_general_ci     |      2 |
| cp866    | DOS Russian                     | cp866_general_ci    |      1 |
| keybcs2  | DOS Kamenicky Czech-Slovak      | keybcs2_general_ci  |      1 |
| macce    | Mac Central European            | macce_general_ci    |      1 |
| macroman | Mac West European               | macroman_general_ci |      1 |
| cp852    | DOS Central European            | cp852_general_ci    |      1 |
| latin7   | ISO 8859-13 Baltic              | latin7_general_ci   |      1 |
| utf8mb4  | UTF-8 Unicode                   | utf8mb4_general_ci  |      4 |
| cp1251   | Windows Cyrillic                | cp1251_general_ci   |      1 |
| utf16    | UTF-16 Unicode                  | utf16_general_ci    |      4 |
| utf16le  | UTF-16LE Unicode                | utf16le_general_ci  |      4 |
| cp1256   | Windows Arabic                  | cp1256_general_ci   |      1 |
| cp1257   | Windows Baltic                  | cp1257_general_ci   |      1 |
| utf32    | UTF-32 Unicode                  | utf32_general_ci    |      4 |
| binary   | Binary pseudo charset           | binary              |      1 |
| geostd8  | GEOSTD8 Georgian                | geostd8_general_ci  |      1 |
| cp932    | SJIS for Windows Japanese       | cp932_japanese_ci   |      2 |
| eucjpms  | UJIS for Windows Japanese       | eucjpms_japanese_ci |      3 |
| gb18030  | China National Standard GB18030 | gb18030_chinese_ci  |      4 |
+----------+---------------------------------+---------------------+--------+
41 rows in set (0.00 sec)

3.3hex()函数

查看字符的16进制

(root@localhost) [python]> select hex('a');
+----------+
| hex('a') |
+----------+
| 61       |
+----------+
1 row in set (0.00 sec)(root@localhost) [python]> select hex('ab');
+-----------+
| hex('ab') |
+-----------+
| 6162      |
+-----------+
1 row in set (0.00 sec)(root@localhost) [python]> select hex('abc');
+------------+
| hex('abc') |
+------------+
| 616263     |
+------------+
1 row in set (0.00 sec)(root@localhost) [python]> select hex('紫');
+------------+
| hex('紫')  |
+------------+
| E7B4AB     |
+------------+
1 row in set (0.00 sec)(root@localhost) [python]> select 0xE7B4AB;
+----------+
| 0xE7B4AB |
+----------+
| 紫       |
+----------+
1 row in set (0.00 sec)(root@localhost) [python]> insert into t values('aaa',0xE7B4AB,0xE7B4AB);
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> select * from t;
+------+------+------+
| a    | b    | c    |
+------+------+------+
| aaa  | 紫   | 紫   |
+------+------+------+
1 row in set (0.00 sec)

3.4cast()函数

CAST函数用于将某种数据类型的表达式显式转换为另一种数据类型。CAST()函数的参数是一个表达式，它包括用AS关键字分隔的源值和目标数据类型。

语法

CAST(value AS datatype)

datatype参数取值

值	描述
DATE	将value转换成'YYYY-MM-DD'格式
DATETIME	将value转换成'YYYY-MM-DD HH：MM：SS'格式
TIME	将value转换成'HH：MM：SS'格式
CHAR	将value转换成CHAR(固定长度的字符串)格式
SIGNED	将value转换成INT(有符号的整数)格式
UNSIGNED	将value转换成INT(无符号的整数)格式
DECIMAL	将value转换成FLOAT(浮点数)格式
BINARY	将value转换成二进制格式

(root@localhost) [python]> SELECT CAST('13.6' AS decimal(9,2));
+------------------------------+
| CAST('13.6' AS decimal(9,2)) |
+------------------------------+
|                        13.60 |
+------------------------------+
1 row in set (0.00 sec)(root@localhost) [python]> select cast(123 as char(1));
+----------------------+
| cast(123 as char(1)) |
+----------------------+
| 1                    |
+----------------------+
1 row in set, 1 warning (0.00 sec)(root@localhost) [python]> select cast(123 as char(10));
+-----------------------+
| cast(123 as char(10)) |
+-----------------------+
| 123                   |
+-----------------------+
1 row in set (0.00 sec)(root@localhost) [python]> select cast('a' as char(10));
+-----------------------+
| cast('a' as char(10)) |
+-----------------------+
| a                     |
+-----------------------+
1 row in set (0.01 sec)(root@localhost) [python]> select cast('a' as char(10) charset gbk);
+-----------------------------------+
| cast('a' as char(10) charset gbk) |
+-----------------------------------+
| a                                 |
+-----------------------------------+
1 row in set (0.00 sec)(root@localhost) [python]> select hex(cast('a' as char(10) charset gbk));
+----------------------------------------+
| hex(cast('a' as char(10) charset gbk)) |
+----------------------------------------+
| 61                                     |
+----------------------------------------+
1 row in set (0.00 sec)(root@localhost) [python]> select hex('a');
+----------+
| hex('a') |
+----------+
| 61       |
+----------+
1 row in set (0.00 sec)(root@localhost) [python]> select hex(cast('紫' as char(10) charset gbk));
+------------------------------------------+
| hex(cast('紫' as char(10) charset gbk))  |
+------------------------------------------+
| D7CF                                     |
+------------------------------------------+
1 row in set (0.00 sec)(root@localhost) [python]> select hex('紫');
+------------+
| hex('紫')  |
+------------+
| E7B4AB     |
+------------+
1 row in set (0.00 sec)(root@localhost) [python]> select 0xD7CF;
+--------+
| 0xD7CF |
+--------+
| ؏       |
+--------+
1 row in set (0.00 sec)(root@localhost) [python]> show create table z\G;
*************************** 1. row ***************************Table: z
Create Table: CREATE TABLE `z` (`a` char(1) DEFAULT NULL,`b` varchar(3) DEFAULT NULL,`c` binary(1) DEFAULT NULL,`d` varbinary(3) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
1 row in set (0.00 sec)ERROR: 
No query specified(root@localhost) [python]> insert into z values('a',0xD7CF,'c',0xD7CF);
ERROR 1366 (HY000): Incorrect string value: '\xD7\xCF' for column 'b' at row 1
(root@localhost) [python]> insert into z values('a',0xE7B4AB,'c',0xD7CF);
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> select * from z;
+------+------+------+------+
| a    | b    | c    | d    |
+------+------+------+------+
| a    | bbb  | c    | ddd  |
| 紫   | bbc  | x    | ooo  |
| a    | 紫   | c    | ؏     |
+------+------+------+------+
3 rows in set (0.00 sec)

从上面看出，varbinary类型不会检测对应的字符是否存在，只会去存16进制的这个值，varchar类型会去检测16进制的值对应的字符是否存在

3.5排序规则collation

(root@localhost) [(none)]> select 'a' = 'a';
+-----------+
| 'a' = 'a' |
+-----------+
|         1 |
+-----------+
1 row in set (0.00 sec)(root@localhost) [(none)]> select 'a' = 'a    ';
+---------------+
| 'a' = 'a    ' |
+---------------+
|             1 |
+---------------+
1 row in set (0.00 sec)(root@localhost) [(none)]> select 'a' = 'A';
+-----------+
| 'a' = 'A' |
+-----------+
|         1 |
+-----------+
1 row in set (0.01 sec)(root@localhost) [(none)]> select 'a' = 'A    ';
+---------------+
| 'a' = 'A    ' |
+---------------+
|             1 |
+---------------+
1 row in set (0.00 sec)(root@localhost) [python]> drop table t;
Query OK, 0 rows affected (0.02 sec)(root@localhost) [python]> create table t (a char(1),unique key(a));
Query OK, 0 rows affected (0.02 sec)(root@localhost) [python]> insert into t values('a');
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> insert into t values('A');
ERROR 1062 (23000): Duplicate entry 'A' for key 'a'
(root@localhost) [python]> insert into t values('a    ');
ERROR 1062 (23000): Duplicate entry 'a' for key 'a'
(root@localhost) [python]> insert into t values('A    ');
ERROR 1062 (23000): Duplicate entry 'A' for key 'a'
(root@localhost) [python]> select * from t;
+------+
| a    |
+------+
| a    |
+------+
1 row in set (0.00 sec)

show charset看到的有一列是Default collation，其中utf8mb4字符集对应的排序规则是utf8mb4_general_ci，ci(case insensitive)表示不区分大小写

3.6对于密码的加密，md5()函数

(root@localhost) [python]> drop table t;
Query OK, 0 rows affected (0.01 sec)(root@localhost) [python]> create table t(password varchar(128));
Query OK, 0 rows affected (0.01 sec)(root@localhost) [python]> insert into t values('aaa');
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> insert into t values('BBB');
Query OK, 1 row affected (0.01 sec)(root@localhost) [python]> insert into t values(md5('aaa'));
Query OK, 1 row affected (0.01 sec)(root@localhost) [python]> insert into t values(md5('BBB'));
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> select * from t;
+----------------------------------+
| password                         |
+----------------------------------+
| aaa                              |
| BBB                              |
| 47bce5c74f589f4867dbd57e9ca9f808 |
| 2bb225f0ba9a58930757a868ed57d9a3 |
+----------------------------------+
4 rows in set (0.00 sec)(root@localhost) [python]> insert into t values(md5(concat('aaa','zs')));
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> insert into t values(md5(concat('BBB','zs')));
Query OK, 1 row affected (0.01 sec)(root@localhost) [python]> select * from t;
+----------------------------------+
| password                         |
+----------------------------------+
| aaa                              |
| BBB                              |
| 47bce5c74f589f4867dbd57e9ca9f808 |
| 2bb225f0ba9a58930757a868ed57d9a3 |
| ebf93b07e04f07d5efea104226ce36f5 |
| 5812c79db401f78da7fd2aaf03f9ca97 |
+----------------------------------+
6 rows in set (0.00 sec)

密码通过加密存储，一般来说也不区分大小写

强制密码区分大小写

(root@localhost) [python]> create table y (password varchar(128) collate utf8mb4_bin,unique key(password));
Query OK, 0 rows affected (0.01 sec)(root@localhost) [python]> insert into y values('a');
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> insert into y values('A');
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> select * from y;
+----------+
| password |
+----------+
| A        |
| a        |
+----------+
2 rows in set (0.00 sec)

3.7upper()和lower()函数

upper()字符串转换成大写，lower()字符串转换成小写

(root@localhost) [python]> select upper('abC');
+--------------+
| upper('abC') |
+--------------+
| ABC          |
+--------------+
1 row in set (0.01 sec)(root@localhost) [python]> select lower('aBC');
+--------------+
| lower('aBC') |
+--------------+
| abc          |
+--------------+
1 row in set (0.01 sec)

3.8concat()和concat_ws()函数

concat()直接把字符串拼接起来，concat_ws()通过指定的符号把字符串拼接起来

(root@localhost) [python]> select concat('a','b','ccc',123);
+---------------------------+
| concat('a','b','ccc',123) |
+---------------------------+
| abccc123                  |
+---------------------------+
1 row in set (0.00 sec)(root@localhost) [python]> select concat_ws('!','a','b','ccc',123);
+----------------------------------+
| concat_ws('!','a','b','ccc',123) |
+----------------------------------+
| a!b!ccc!123                      |
+----------------------------------+
1 row in set (0.00 sec)

3.9lpad()和rpad()函数

lpad()左填充，rpad()右填充

(root@localhost) [python]> select lpad('aaa',8,'!');
+-------------------+
| lpad('aaa',8,'!') |
+-------------------+
| !!!!!aaa          |
+-------------------+
1 row in set (0.00 sec)(root@localhost) [python]> select rpad('aaa',8,'!');
+-------------------+
| rpad('aaa',8,'!') |
+-------------------+
| aaa!!!!!          |
+-------------------+
1 row in set (0.00 sec)

4.enum&set类型

枚举类型常用于性别等distinct的值不多的情况

(root@localhost) [python]> drop table y;
Query OK, 0 rows affected (0.01 sec)(root@localhost) [python]> create table y (sex enum('male','female'));
Query OK, 0 rows affected (0.01 sec)(root@localhost) [python]> 
(root@localhost) [python]> insert into y values('male');
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> insert into y values('male11');
ERROR 1265 (01000): Data truncated for column 'sex' at row 1
(root@localhost) [python]> insert into y values('female');
Query OK, 1 row affected (0.00 sec)(root@localhost) [python]> insert into y values('zhs');
ERROR 1265 (01000): Data truncated for column 'sex' at row 1
(root@localhost) [python]> select * from y;
+--------+
| sex    |
+--------+
| male   |
| female |
+--------+
2 rows in set (0.01 sec)

5.时间类型

常用日期类型：datetime和timestamp

5.1日期函数

5.1.1now()函数

unix_timestamp(now())是1970-01-01 00:00:00到现在的秒数

(root@localhost) [dbt3]> select now();
+---------------------+
| now()               |
+---------------------+
| 2024-03-21 13:21:05 |
+---------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select unix_timestamp(now());
+-----------------------+
| unix_timestamp(now()) |
+-----------------------+
|            1710998483 |
+-----------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select timestamp(now());
+---------------------+
| timestamp(now())    |
+---------------------+
| 2024-03-21 13:21:29 |
+---------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> create table z (a datetime,b timestamp);
Query OK, 0 rows affected (0.01 sec)(root@localhost) [dbt3]> insert into z values(now(),now());
Query OK, 1 row affected (0.00 sec)(root@localhost) [dbt3]> select * from z;
+---------------------+---------------------+
| a                   | b                   |
+---------------------+---------------------+
| 2024-03-21 13:26:50 | 2024-03-21 13:26:50 |
+---------------------+---------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> show variables like 'time_zone';
+---------------+--------+
| Variable_name | Value  |
+---------------+--------+
| time_zone     | SYSTEM |
+---------------+--------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> set time_zone = '+0:00';
Query OK, 0 rows affected (0.00 sec)(root@localhost) [dbt3]> select * from z;
+---------------------+---------------------+
| a                   | b                   |
+---------------------+---------------------+
| 2024-03-21 13:26:50 | 2024-03-21 05:26:50 |
+---------------------+---------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select now(10);
ERROR 1426 (42000): Too-big precision 10 specified for 'now'. Maximum is 6.
(root@localhost) [dbt3]> select now(6);
+----------------------------+
| now(6)                     |
+----------------------------+
| 2024-03-21 05:29:22.432329 |
+----------------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select now(3);
+-------------------------+
| now(3)                  |
+-------------------------+
| 2024-03-21 05:29:36.677 |
+-------------------------+
1 row in set (0.00 sec)

5.1.2now()和sysdate()的区别

now()表示该条sql执行开始的时间，sysdate()表示执行到该函数的时间

(root@localhost) [dbt3]> select now(),sysdate(),sleep(4),now(),sysdate();
+---------------------+---------------------+----------+---------------------+---------------------+
| now()               | sysdate()           | sleep(4) | now()               | sysdate()           |
+---------------------+---------------------+----------+---------------------+---------------------+
| 2024-03-21 05:34:46 | 2024-03-21 05:34:46 |        0 | 2024-03-21 05:34:46 | 2024-03-21 05:34:50 |
+---------------------+---------------------+----------+---------------------+---------------------+
1 row in set (4.00 sec)(root@localhost) [dbt3]> select now(6),sysdate(6);
+----------------------------+----------------------------+
| now(6)                     | sysdate(6)                 |
+----------------------------+----------------------------+
| 2024-03-21 05:35:58.930067 | 2024-03-21 05:35:58.930234 |
+----------------------------+----------------------------+
1 row in set (0.00 sec)

5.1.3date_add()和date_sub()函数

时间加减函数

(root@localhost) [dbt3]> set time_zone='+8:00';
Query OK, 0 rows affected (0.00 sec)(root@localhost) [dbt3]> select now();
+---------------------+
| now()               |
+---------------------+
| 2024-03-21 13:41:15 |
+---------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select date_add(now(),interval 1 day);
+--------------------------------+
| date_add(now(),interval 1 day) |
+--------------------------------+
| 2024-03-22 13:42:18            |
+--------------------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select date_add(now(),interval -2 day);
+---------------------------------+
| date_add(now(),interval -2 day) |
+---------------------------------+
| 2024-03-19 13:42:33             |
+---------------------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select date_add(now(),interval -2 hour);
+----------------------------------+
| date_add(now(),interval -2 hour) |
+----------------------------------+
| 2024-03-21 11:43:06              |
+----------------------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select date_add(now(),interval -2 minute);
+------------------------------------+
| date_add(now(),interval -2 minute) |
+------------------------------------+
| 2024-03-21 13:41:25                |
+------------------------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select date_sub(now(),interval 2 day);
+--------------------------------+
| date_sub(now(),interval 2 day) |
+--------------------------------+
| 2024-03-19 14:45:05            |
+--------------------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select date_sub(now(),interval -2 day);
+---------------------------------+
| date_sub(now(),interval -2 day) |
+---------------------------------+
| 2024-03-23 14:45:10             |
+---------------------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select date_sub(now(),interval 4 hour);
+---------------------------------+
| date_sub(now(),interval 4 hour) |
+---------------------------------+
| 2024-03-21 10:45:42             |
+---------------------------------+
1 row in set (0.01 sec)

5.1.4date_format()函数

语法

DATE_FORMAT(date,format)

date 参数是合法的日期，format 规定日期/时间的输出格式。可用的格式如下：

格式	描述
%a	缩写星期名
%b	缩写月名
%c	月，数值
%D	带有英文前缀的月中的天
%d	月的天，数值(00-31)
%e	月的天，数值(0-31)
%f	微秒
%H	小时 (00-23)
%h	小时 (01-12)
%I	小时 (01-12)
%i	分钟，数值(00-59)
%j	年的天 (001-366)
%k	小时 (0-23)
%l	小时 (1-12)
%M	月名
%m	月，数值(00-12)
%p	AM 或 PM
%r	时间，12-小时（hh:mm:ss AM 或 PM）
%S	秒(00-59)
%s	秒(00-59)
%T	时间, 24-小时 (hh:mm:ss)
%U	周 (00-53) 星期日是一周的第一天
%u	周 (00-53) 星期一是一周的第一天
%V	周 (01-53) 星期日是一周的第一天，与 %X 使用
%v	周 (01-53) 星期一是一周的第一天，与 %x 使用
%W	星期名
%w	周的天（0=星期日, 6=星期六）
%X	年，其中的星期日是周的第一天，4 位，与 %V 使用
%x	年，其中的星期一是周的第一天，4 位，与 %v 使用
%Y	年，4 位
%y	年，2 位

(root@localhost) [dbt3]> select date_format(now(),'%Y/%m/%s %H.%i.%S');
+----------------------------------------+
| date_format(now(),'%Y/%m/%s %H.%i.%S') |
+----------------------------------------+
| 2024/03/25 13.49.25                    |
+----------------------------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select date_format(now(),'%a');
+-------------------------+
| date_format(now(),'%a') |
+-------------------------+
| Thu                     |
+-------------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select date_format(now(),'%b');
+-------------------------+
| date_format(now(),'%b') |
+-------------------------+
| Mar                     |
+-------------------------+
1 row in set (0.00 sec)(root@localhost) [dbt3]> select date_format(now(),'%W');
+-------------------------+
| date_format(now(),'%W') |
+-------------------------+
| Thursday                |
+-------------------------+
1 row in set (0.00 sec)

6.json类型

json类型跟python中的字典类似

(root@localhost) [dbt3]> create table userjson(uid bigint auto_increment primary key,data json);
Query OK, 0 rows affected (0.01 sec)(root@localhost) [dbt3]> show create table userjson\G
*************************** 1. row ***************************Table: userjson
Create Table: CREATE TABLE `userjson` (`uid` bigint(20) NOT NULL AUTO_INCREMENT,`data` json DEFAULT NULL,PRIMARY KEY (`uid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
1 row in set (0.00 sec)(root@localhost) [dbt3]> INSERT INTO userjson(uid,data)VALUES (NULL,'{"name":"David","address": "Shanghai"}');
Query OK, 1 row affected (0.04 sec)(root@localhost) [dbt3]> INSERT INTO userjson(uid,data)VALUES (NULL,'{"name":"Jim","passport":"E02318883"}');
Query OK, 1 row affected (0.00 sec)(root@localhost) [dbt3]> select * from userjson;
+-----+------------------------------------------+
| uid | data                                     |
+-----+------------------------------------------+
|   1 | {"name": "David", "address": "Shanghai"} |
|   2 | {"name": "Jim", "passport": "E02318883"} |
+-----+------------------------------------------+
2 rows in set (0.00 sec)

6.1json类型相关函数

6.1.1json_extract()函数

(root@localhost) [dbt3]> select uid,json_extract(data,'$.name') from userjson;
+-----+-----------------------------+
| uid | json_extract(data,'$.name') |
+-----+-----------------------------+
|   1 | "David"                     |
|   2 | "Jim"                       |
+-----+-----------------------------+
2 rows in set (0.00 sec)(root@localhost) [dbt3]> select uid,json_unquote(json_extract(data,'$.name')) from userjson;
+-----+-------------------------------------------+
| uid | json_unquote(json_extract(data,'$.name')) |
+-----+-------------------------------------------+
|   1 | David                                     |
|   2 | Jim                                       |
+-----+-------------------------------------------+
2 rows in set (0.00 sec)(root@localhost) [dbt3]> select uid,data->'$.name' from userjson;
+-----+----------------+
| uid | data->'$.name' |
+-----+----------------+
|   1 | "David"        |
|   2 | "Jim"          |
+-----+----------------+
2 rows in set (0.00 sec)(root@localhost) [dbt3]> select uid,data->>'$.name' from userjson;
+-----+-----------------+
| uid | data->>'$.name' |
+-----+-----------------+
|   1 | David           |
|   2 | Jim             |
+-----+-----------------+
2 rows in set (0.00 sec)(root@localhost) [dbt3]> select uid,data->>'$.passport' from userjson;
+-----+---------------------+
| uid | data->>'$.passport' |
+-----+---------------------+
|   1 | NULL                |
|   2 | E02318883           |
+-----+---------------------+
2 rows in set (0.00 sec)

6.1.2json_remove()函数

(root@localhost) [dbt3]> select * from userjson;
+-----+------------------------------------------+
| uid | data                                     |
+-----+------------------------------------------+
|   1 | {"name": "David", "address": "Shanghai"} |
|   2 | {"name": "Jim", "passport": "E02318883"} |
+-----+------------------------------------------+
2 rows in set (0.00 sec)(root@localhost) [dbt3]> select uid,json_remove(data,'$.name') from userjson;
+-----+----------------------------+
| uid | json_remove(data,'$.name') |
+-----+----------------------------+
|   1 | {"address": "Shanghai"}    |
|   2 | {"passport": "E02318883"}  |
+-----+----------------------------+
2 rows in set (0.01 sec)(root@localhost) [dbt3]> select uid,json_remove(data,'$.passport') from userjson;
+-----+------------------------------------------+
| uid | json_remove(data,'$.passport')           |
+-----+------------------------------------------+
|   1 | {"name": "David", "address": "Shanghai"} |
|   2 | {"name": "Jim"}                          |
+-----+------------------------------------------+
2 rows in set (0.00 sec)