MySQL数据定义语句

Posted 2020-06-14

mysql数据定义语句主要是创建、修改、删除表，增加，修改，删除字段的操作

创建表：
CREATE TABLE 表名(属性名 数据类型 约束条件，
属性名 数据类型 约束条件，
属性名 数据类型 约束条件，
属性名 数据类型 ，
);

完整约束条件：
PRIMARY KEY 主键
FOREIGN KEY 外键
NOT NULL 非空
UNIQUE 唯一键
AUTO_INCREMENT 自增键（mysql特色）
DEFAULT 设置默认值


1、创建表test1

mysql> create table test1(id int not null primary key,
-> name varchar(20) not null);
Query OK, 0 rows affected (0.00 sec)

 

mysql> desc test1;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name | varchar(20) | NO | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)

 

2、设置多字段主键

mysql> create table test2(id int not null,
-> name int not null,
-> primary key(id,name));
Query OK, 0 rows affected (0.00 sec)

mysql> desc test2;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name | int(11) | NO | PRI | NULL | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)

 

3、设置外键

mysql> create table test4(id int primary key,
-> name int not null,
-> constraint fk foreign key(id,name)
-> references test3(id,name));
Query OK, 0 rows affected (0.00 sec)

 

4、查看表结构

mysql> desc test4;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name | int(11) | NO | | NULL | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.01 sec)

 

5、查看表详细语法

mysql> show create table test4\G
*************************** 1. row ***************************
Table: test4
Create Table: CREATE TABLE `test4` (
`id` int(11) NOT NULL,
`name` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `fk` (`id`,`name`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

 

6、修改表名

mysql> alter table test4 rename test004;
Query OK, 0 rows affected (0.00 sec)

 

7、修改字段数据类型

mysql> alter table test1 modify name varchar(30);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

 

8、修改字段名

mysql> alter table test1 change name mingzi varchar(20);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

 

9、增加字段

mysql> alter table test1 add address varchar(60);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

 

10、将增加字段放在首位

mysql> alter table test1 add user int first; 
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0

 

11、将增加字段放在指定位置

mysql> alter table test1 add home int after id; 
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0

 

12、删除字段

mysql> alter table test1 drop mingzi;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

 

13、修改字段位置

mysql> alter table test1 modify address varchar(20) after id;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0

 

13、修改表引擎

mysql> alter table test1 engine=‘innodb‘;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

 

14、删除外键

mysql> alter table test004 drop foreign key fk; 
Query OK, 0 rows affected (0.06 sec)
Records: 0 Duplicates: 0 Warnings: 0

 

15、删除表

mysql> drop table test004;
Query OK, 0 rows affected (0.00 sec)

 

16、创建数据库

mysql> create database test1;
Query OK, 1 row affected (0.00 sec)

 

参考书籍：《MySQL入门很简单》