MySQL学习——操作数据库（增删改查）（二）

时间：2017-12-05 22:40:58 阅读：241 评论：0 收藏：0 [点我收藏+]

标签：update res nbsp prim pytho const text ref record

修改表

　　修改表是指修改数据库中已经存在的表的定义，修改表比重新定义表简单，不需要重新加载数据，也不会影响正在进行的服务，mysql中通过ALTER TABLE语句来修改表。修改表包括修改表名，修改字段数据类型，修改字段名，增减字段，修改字段的排列位置，更改默认存储引擎和删除表的外键约束等。

1.修改表名：

　　ALTER TABLE 旧表名 RENAME 新表名；

将example0 表改名为user表：
mysql>
mysql> desc example0;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(20) | YES  |     | NULL    |       |
| sex   | tinyint(1)  | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> alter table example0 rename user;
Query OK, 0 rows affected (0.25 sec)

mysql> desc example0;
ERROR 1146 (42S02): Table ‘text.example0‘ doesn‘t exist
mysql> desc user;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(20) | YES  |     | NULL    |       |
| sex   | tinyint(1)  | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.01 sec)

mysql>

2,。修改字段数据类型：

　　ALTER TABLE 表名 MODIFY 属性名数据类型；

修改user表中name字段的数据类型

mysql>
mysql> desc user;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(20) | YES  |     | NULL    |       |
| sex   | tinyint(1)  | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> alter table user modify name varchar(30);
Query OK, 0 rows affected (0.12 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(30) | YES  |     | NULL    |       |
| sex   | tinyint(1)  | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql>

3.修改字段名：

　　ALTER TABLE 表名 CHANGE 旧属性名新属性名新数据类型；

1.只修改字段名：
    将example1表中stu_name 字段改名为name，且不改变数据类型：

mysql>
mysql> desc example1;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| stu_id   | int(11)     | NO   | PRI | NULL    |       |
| stu_name | varchar(20) | YES  |     | NULL    |       |
| stu_sex  | tinyint(1)  | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> alter table example1 change stu_name  name varchar(20);
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc example1;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| stu_id  | int(11)     | NO   | PRI | NULL    |       |
| name    | varchar(20) | YES  |     | NULL    |       |
| stu_sex | tinyint(1)  | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql>




2.修改字段名和字段数据类型
    将example1表中stu_sex字段改名为sex，且数据类型改为INT（2）：

mysql>
mysql> desc example1;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| stu_id  | int(11)     | NO   | PRI | NULL    |       |
| name    | varchar(20) | YES  |     | NULL    |       |
| stu_sex | tinyint(1)  | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> alter table example1 stu_sex sex int(2);
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 ‘stu_sex sex int(2)‘ at line 1
mysql> alter table example1 change stu_sex sex int(2);
Query OK, 0 rows affected (0.95 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc example1;
+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| stu_id | int(11)     | NO   | PRI | NULL    |       |
| name   | varchar(20) | YES  |     | NULL    |       |
| sex    | int(2)      | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql>

4.增加字段

　　ALTER TABLE 表名 ADD 属性名1 数据类型【完整约束条件】【first | after 属性名2】；

1.增加无完整性约束条件的字段：
    将user表中增加一个没有完整性约束条件约束的phone字段

mysql>
mysql> desc user;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(30) | YES  |     | NULL    |       |
| sex   | tinyint(1)  | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> alter table user add phone varvhar(20);
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 ‘varvhar(20)‘ at line 1
mysql> alter table user add phone varchar(20);
Query OK, 0 rows affected (0.68 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(30) | YES  |     | NULL    |       |
| sex   | tinyint(1)  | YES  |     | NULL    |       |
| phone | varchar(20) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql>


2.增加有完整性约束条件的字段：
    在user表中增加一个有非空约束的age字段
mysql>
mysql> alter table user add age int(4) not null;
Query OK, 0 rows affected (1.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(30) | YES  |     | NULL    |       |
| sex   | tinyint(1)  | YES  |     | NULL    |       |
| phone | varchar(20) | YES  |     | NULL    |       |
| age   | int(4)      | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql>


3.表的第一个位置增加字段：
        在user表中第一个位置增加num字段，并设置num字段为主键
mysql>
mysql> alter table user add num int(8) primary key first;
Query OK, 0 rows affected (0.76 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| num   | int(8)      | NO   | PRI | NULL    |       |
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(30) | YES  |     | NULL    |       |
| sex   | tinyint(1)  | YES  |     | NULL    |       |
| phone | varchar(20) | YES  |     | NULL    |       |
| age   | int(4)      | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
6 rows in set (0.01 sec)

mysql>


4.表的指定位置之后增加字段
    在user表的phone字段后加address字段，并设置address字段为非空：
mysql>
mysql> alter table user add address varchar(30) not null after phone;
Query OK, 0 rows affected (0.74 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| num     | int(8)      | NO   | PRI | NULL    |       |
| id      | int(11)     | YES  |     | NULL    |       |
| name    | varchar(30) | YES  |     | NULL    |       |
| sex     | tinyint(1)  | YES  |     | NULL    |       |
| phone   | varchar(20) | YES  |     | NULL    |       |
| address | varchar(30) | NO   |     | NULL    |       |
| age     | int(4)      | NO   |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
7 rows in set (0.00 sec)

mysql>

5.删除字段：

　　ALTER TABLE 表名 DROP 属性名；

将user表中删除id字段：

mysql>
mysql> desc user;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| num     | int(8)      | NO   | PRI | NULL    |       |
| id      | int(11)     | YES  |     | NULL    |       |
| name    | varchar(30) | YES  |     | NULL    |       |
| sex     | tinyint(1)  | YES  |     | NULL    |       |
| phone   | varchar(20) | YES  |     | NULL    |       |
| address | varchar(30) | NO   |     | NULL    |       |
| age     | int(4)      | NO   |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
7 rows in set (0.00 sec)

mysql> alter table user drop id;
Query OK, 0 rows affected (0.60 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| num     | int(8)      | NO   | PRI | NULL    |       |
| name    | varchar(30) | YES  |     | NULL    |       |
| sex     | tinyint(1)  | YES  |     | NULL    |       |
| phone   | varchar(20) | YES  |     | NULL    |       |
| address | varchar(30) | NO   |     | NULL    |       |
| age     | int(4)      | NO   |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

mysql>

6.修改字段的排列位置：

　　ALTER TABLE 表名 MODIFY 属性名1 数据类型 FIRST | AFTER 属性名2；

1.字段修改到第一个位置：
    将user表中name字段修改为该表的第一个字段
mysql> desc user;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| num     | int(8)      | NO   | PRI | NULL    |       |
| name    | varchar(30) | YES  |     | NULL    |       |
| sex     | tinyint(1)  | YES  |     | NULL    |       |
| phone   | varchar(20) | YES  |     | NULL    |       |
| address | varchar(30) | NO   |     | NULL    |       |
| age     | int(4)      | NO   |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

mysql> alter table user modify name varchar(30) first;
Query OK, 0 rows affected (0.73 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name    | varchar(30) | YES  |     | NULL    |       |
| num     | int(8)      | NO   | PRI | NULL    |       |
| sex     | tinyint(1)  | YES  |     | NULL    |       |
| phone   | varchar(20) | YES  |     | NULL    |       |
| address | varchar(30) | NO   |     | NULL    |       |
| age     | int(4)      | NO   |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

mysql>


2.字段修改到指定位置
    将user表中sex字段修改到age字段之后;
mysql>
mysql> alter table user modify sex tinyint(1) after age;
Query OK, 0 rows affected (0.63 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc user;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name    | varchar(30) | YES  |     | NULL    |       |
| num     | int(8)      | NO   | PRI | NULL    |       |
| phone   | varchar(20) | YES  |     | NULL    |       |
| address | varchar(30) | NO   |     | NULL    |       |
| age     | int(4)      | NO   |     | NULL    |       |
| sex     | tinyint(1)  | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

mysql>

7.更改表的存储引擎：

　　ALTER TABLE 表名 ENGINE = 存储引擎名；

将user表的存储引擎改为MyISAM：
mysql>
mysql> show create table user\G
*************************** 1. row ***************************
       Table: user
Create Table: CREATE TABLE `user` (
  `name` varchar(30) DEFAULT NULL,
  `num` int(8) NOT NULL,
  `phone` varchar(20) DEFAULT NULL,
  `address` varchar(30) NOT NULL,
  `age` int(4) NOT NULL,
  `sex` tinyint(1) DEFAULT NULL,
  PRIMARY KEY (`num`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql> alter table user engine=MyISAM;
Query OK, 0 rows affected (0.37 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table user\G
*************************** 1. row ***************************
       Table: user
Create Table: CREATE TABLE `user` (
  `name` varchar(30) DEFAULT NULL,
  `num` int(8) NOT NULL,
  `phone` varchar(20) DEFAULT NULL,
  `address` varchar(30) NOT NULL,
  `age` int(4) NOT NULL,
  `sex` tinyint(1) DEFAULT NULL,
  PRIMARY KEY (`num`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql>

8.删除表的外键约束：

　　ALTER TABLE 表名 DROP FOREIGN KEY 外键别名；

删除表example3的外键约束


alter table example3 drop foreign key c_fk;

删除表：

　　删除表是指删除数据库中已经存在的表，删除表时，会删除表中的所有数据，在删除表时要特别注意，mysql中通过DROP TABLE语句来删除表，由于创建表时可能存在外键约束，一些表成为了与之关联的表的父表，要删除这些表，情况比较复杂。

删除当前存在的example5表
    DROP TABLE example5；

注：删除一个表时，表中的所有数据也会被删除，因此，在删除表的时候一定要慎重，做好先备份在删除。



删除被其他表关联的父表
    在删除其他表关联的父表时，先删除关联外键，在删除表

示例测试：

技术分享图片

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

mysql> use example;
Database changed
mysql>
mysql>
mysql> create table student(num int(10) not null unique primary key,
    -> name varchar(20) not null,
    -> sex varchar(4) not null,
    -> birthday datetime,
    -> address varchar(50)
    -> );
Query OK, 0 rows affected (0.42 sec)

mysql> desc student;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| num      | int(10)     | NO   | PRI | NULL    |       |
| name     | varchar(20) | NO   |     | NULL    |       |
| sex      | varchar(4)  | NO   |     | NULL    |       |
| birthday | datetime    | YES  |     | NULL    |       |
| address  | varchar(50) | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> create table grade(id int(10) not null unique primary key auto_increment,
    -> course varchar(10) not null,
    -> s_num int(10) not null,
    -> grade varchar(4),
    -> CONSTRAINT grade_fk FOREIGN KEY(s_num)
    -> REFERENCES student(num)
    -> );
Query OK, 0 rows affected (1.03 sec)

mysql>
mysql>
mysql> show create table grade\G
*************************** 1. row ***************************
       Table: grade
Create Table: CREATE TABLE `grade` (
  `id` int(10) NOT NULL AUTO_INCREMENT,
  `course` varchar(10) NOT NULL,
  `s_num` int(10) NOT NULL,
  `grade` varchar(4) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `id` (`id`),
  KEY `grade_fk` (`s_num`),
  CONSTRAINT `grade_fk` FOREIGN KEY (`s_num`) REFERENCES `student` (`num`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql>
mysql> alter table grade modify course varchar(20);
Query OK, 0 rows affected (1.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql> desc grade;
+--------+-------------+------+-----+---------+----------------+
| Field  | Type        | Null | Key | Default | Extra          |
+--------+-------------+------+-----+---------+----------------+
| id     | int(10)     | NO   | PRI | NULL    | auto_increment |
| course | varchar(20) | YES  |     | NULL    |                |
| s_num  | int(10)     | NO   | MUL | NULL    |                |
| grade  | varchar(4)  | YES  |     | NULL    |                |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql> alter table grade modify s_num int(10) after id;
Query OK, 0 rows affected (0.82 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc grade;
+--------+-------------+------+-----+---------+----------------+
| Field  | Type        | Null | Key | Default | Extra          |
+--------+-------------+------+-----+---------+----------------+
| id     | int(10)     | NO   | PRI | NULL    | auto_increment |
| s_num  | int(10)     | YES  | MUL | NULL    |                |
| course | varchar(20) | YES  |     | NULL    |                |
| grade  | varchar(4)  | YES  |     | NULL    |                |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql> alter table grade change grade score varchar(4);
Query OK, 0 rows affected (0.15 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql> desc grade;
+--------+-------------+------+-----+---------+----------------+
| Field  | Type        | Null | Key | Default | Extra          |
+--------+-------------+------+-----+---------+----------------+
| id     | int(10)     | NO   | PRI | NULL    | auto_increment |
| s_num  | int(10)     | YES  | MUL | NULL    |                |
| course | varchar(20) | YES  |     | NULL    |                |
| score  | varchar(4)  | YES  |     | NULL    |                |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql>
mysql> alter table grade engine = MyISAM;
ERROR 1217 (23000): Cannot delete or update a parent row: a foreign key constraint fails
mysql> alter table grade drop foreign key grade_fk;
Query OK, 0 rows affected (0.12 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table grade engine = MyISAM;
Query OK, 0 rows affected (0.50 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql> show create table grade\G
*************************** 1. row ***************************
       Table: grade
Create Table: CREATE TABLE `grade` (
  `id` int(10) NOT NULL AUTO_INCREMENT,
  `s_num` int(10) DEFAULT NULL,
  `course` varchar(20) DEFAULT NULL,
  `score` varchar(4) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `id` (`id`),
  KEY `grade_fk` (`s_num`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql>
mysql> alter table grade engine=MyISAM;
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql>
mysql> alter table student drop address;
Query OK, 0 rows affected (0.72 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table student add phone int(10);
Query OK, 0 rows affected (0.63 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc student;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| num      | int(10)     | NO   | PRI | NULL    |       |
| name     | varchar(20) | NO   |     | NULL    |       |
| sex      | varchar(4)  | NO   |     | NULL    |       |
| birthday | datetime    | YES  |     | NULL    |       |
| phone    | int(10)     | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

mysql> alter table grade rename gradeinfo;
Query OK, 0 rows affected (0.01 sec)

mysql>
mysql>
mysql> show tables;
+-------------------+
| Tables_in_example |
+-------------------+
| gradeinfo         |
| student           |
+-------------------+
2 rows in set (0.00 sec)

mysql> drop table studnet;
ERROR 1051 (42S02): Unknown table ‘example.studnet‘
mysql> drop table student;
Query OK, 0 rows affected (0.25 sec)

mysql> show tables;
+-------------------+
| Tables_in_example |
+-------------------+
| gradeinfo         |
+-------------------+
1 row in set (0.01 sec)

mysql>

MySQL学习——操作数据库（增删改查）（二）

标签：update res nbsp prim pytho const text ref record

原文地址：http://www.cnblogs.com/yuxiang-qiwa/p/7989689.html

踩

(0)

评论一句话评论（0）

分享档案

更多>

2021年07月29日 (22)
2021年07月28日 (40)
2021年07月27日 (32)
2021年07月26日 (79)
2021年07月23日 (29)
2021年07月22日 (30)
2021年07月21日 (42)
2021年07月20日 (16)
2021年07月19日 (90)
2021年07月16日 (35)

周排行