标签:存储 records 删除表 value 主键 auto mod data modify
1. 使用主键约束主键约束要求主键列的数据唯一,并且不允许为空。
1). 单字段主键
语法: 字段名 数据类型 PRIMARY KEY [默认值]
mysql> create database test01; #创建库
Query OK, 1 row affected (0.00 sec)
mysql> use test01; #进入所创建的库
Database changed
mysql> create table test1
-> (
-> id INT(11) PRIMARY KEY,
-> name VARCHAR(25),
-> deptID INT(11),
-> salary FLOAT
-> );
Query OK, 0 rows affected (0.04 sec)
查看数据表的结构 DESCRIBE 表名; 或 DESC 表名;
2). 在定义完所有列之后指定主键
语法:[CONSTRAINT <约束名>] PRIMARY KEY [字段名]
mysql> create table test2
-> (
-> id INT(11),
-> name VARCHAR(25),
-> deptID INT(11),
-> salary FLOAT,
-> PRIMARY KEY(id)
-> );
Query OK, 0 rows affected (0.00 sec)
3). 多字段联合主键
语法:PRIMARY KEY [字段1,字段2,....]
mysql> create table test3
-> (
-> id INT(11),
-> name VARCHAR(25),
-> deptID INT(11),
-> salary FLOAT,
-> PRIMARY KEY(id)
-> );
Query OK, 0 rows affected (0.00 sec)
2.设置表的属性值自动增加
语法:字段名 数据类型 AUTO_INCREMENT
mysql> create table test5
-> (
-> id INT(11) PRIMARY KEY AUTO_INCREMENT,
-> name VARCHAR(25) NOT NULL,
-> deptId INT(11),
-> salary FLOAT
-> );
Query OK, 0 rows affected (0.01 sec)
mysql> INSERT INTO test5(name,salary)
-> VALUES(‘lucy‘,1000),(‘lura‘,1200),(‘kevin‘,1500);
mysql> SELECT * FROM test5;
+----+-------+--------+--------+
| id | name | deptId | salary |
+----+-------+--------+--------+
| 1 | lucy | NULL | 1000 |
| 2 | lura | NULL | 1200 |
| 3 | kevin | NULL | 1500 |
+----+-------+--------+--------+
3 rows in set (0.00 sec)
3.查看表的详细结构语句
语法:SHOW CREATE TABLE <表名\G>
4.修改数据表名
语法:ALTER TABLE <旧表名> RENAME [TO] <新表名>.
5.修改字段的数据类型
语法:ALTER TABLE <表名> MODIFY <字段名> <数据类型>
6.修改字段名
语法:ALTER TABLE <表名> CHANGE<旧字段名><新字段名> <新数据类型>
7. 添加字段
语法:ALTER TABLE <表名> ADD <新字段名><数据类型> [约束条件] [FIRST|AFTER 已存在字段名]
mysql> desc test2;
+--------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name11 | varchar(30) | YES | | NULL | |
| deptID | int(11) | YES | | NULL | |
| salary | float | YES | | NULL | |
+--------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql> ALTER TABLE test2 ADD column1 VARCHAR(12) not null;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc test2;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name11 | varchar(30) | YES | | NULL | |
| deptID | int(11) | YES | | NULL | |
| salary | float | YES | | NULL | |
| column1 | varchar(12) | NO | | NULL | |
+---------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
也可以这样:
8.删除字段
mysql> ALTER TABLE tb_dept1 DROP column2;
9.修改字段的排列位置
语法:ALTER TABLE <表名> MODIFY <字段名> <数据类型> FIRST | AFTER <字段2>
10.更改表的存储引擎
11.删除表的外键约束
语法:ALTER TABLE <表名> DROP FOREIGN KEY <外键约束名>
mysql> create table test6
-> (
-> id INT(11) PRIMARY KEY,
-> name VARCHAR(25),
-> deptID INT(11),
-> salary FLOAT,
-> CONSTRAINT fk_emp_dept FOREIGN KEY (deptId) REFERENCES test1(id)
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> show create table test6\g
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test6 | CREATE TABLE `test6` (
`id` int(11) NOT NULL,
`name` varchar(25) DEFAULT NULL,
`deptID` int(11) DEFAULT NULL,
`salary` float DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fk_emp_dept` (`deptID`),
CONSTRAINT `fk_emp_dept` FOREIGN KEY (`deptID`) REFERENCES `test1` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> ALTER TABLE test6 DROP FOREIGN KEY fk_emp_dept;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show create table test6\g
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test6 | CREATE TABLE `test6` (
`id` int(11) NOT NULL,
`name` varchar(25) DEFAULT NULL,
`deptID` int(11) DEFAULT NULL,
`salary` float DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fk_emp_dept` (`deptID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
12.删除数据表
语法:DROP TABLE [IF EXISTS]表1,表2
1)先创建ts3
mysql> create table ts3
-> (
-> id INT(11) PRIMARY KEY,
-> name VARCHAR(22),
-> location VARCHAR(50)
-> );
Query OK, 0 rows affected (0.01 sec)
2)创建test7
mysql> create table test7
-> (
-> id INT(11) PRIMARY KEY,
-> name VARCHAR(25),
-> deptId INT(11),
-> salary FLOAT,
-> CONSTRAINT fk_emp_dept FOREIGN KEY(deptId) REFERENCES ts3(id)
-> );
Query OK, 0 rows affected (0.00 sec)
3)直接删除父表ts3
就可以看见在外键的约束时,主表不能直接删除。
4)解除关联子表test7的外键约束
mysql> ALTER TABLE test7 DROP FOREIGN KEY fk_emp_dept;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
5)这样主表就可以删除了
mysql> drop table ts3;
Query OK, 0 rows affected (0.01 sec)
标签:存储 records 删除表 value 主键 auto mod data modify
原文地址:https://blog.51cto.com/14306186/2487782