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mysql表中数据表的各种操作，创建表、添加各类约束、查看表结构、修改和删除表。这次带你捋清楚，从头再走一遍。

实验目的

创建、修改和删除表，掌握数据表的基本操作。

实验结果

创建数据库company，按照以下两个表结构在company数据库中创建两个数据表offices和employees。

表1（offices）：

表2（employees）：

实验过程

1、登录数据库

PS C:\Users\22768> mysql -uroot -pEnter password: *************Welcome to the MySQL monitor.  Commands end with ; or \g.Your MySQL connection id is 9Server version: 8.0.29 MySQL Community Server - GPLCopyright (c) 2000, 2021, Oracle and/or its affiliates.Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql>

2、创建数据库

创建数据库company：

mysql> create database company;Query OK, 1 row affected (0.01 sec)mysql>

3、进入数据库

切换到我们新创建的数据库中；

mysql> use company;Database changedmysql>

4、创建表一

创建数据表offices；

mysql> create table offices (officeCode int not null unique, city varchar(50) not null, address varchar(50) not null, country varchar(50) not null, postalCode varchar(15) not null, primary key (officeCode));Query OK, 0 rows affected (0.06 sec)mysql> desc offices;+------------+-------------+------+-----+---------+-------+| Field      | Type        | Null | Key | Default | Extra |+------------+-------------+------+-----+---------+-------+| officeCode | int         | NO   | PRI | NULL    |       || city       | varchar(50) | NO   |     | NULL    |       || address    | varchar(50) | NO   |     | NULL    |       || country    | varchar(50) | NO   |     | NULL    |       || postalCode | varchar(15) | NO   |     | NULL    |       |+------------+-------------+------+-----+---------+-------+5 rows in set (0.01 sec)mysql>

5、创建表二

创建数据库employees；

mysql> create table employees (employeeNumber int not null primary key auto_increment, lastname varchar(50) not null, firstname varchar(50) not null, mobile varchar(25) not null, officeCode int not null, jobTitle varchar(50) not null, birth datetime, note varchar(255), sex varchar(5), constraint office_fk foreign key(officeCode) references offices(officeCode));Query OK, 0 rows affected (0.05 sec)mysql> desc employees;+----------------+--------------+------+-----+---------+----------------+| Field          | Type         | Null | Key | Default | Extra          |+----------------+--------------+------+-----+---------+----------------+| employeeNumber | int          | NO   | PRI | NULL    | auto_increment || lastname       | varchar(50)  | NO   |     | NULL    |                || firstname      | varchar(50)  | NO   |     | NULL    |                || mobile         | varchar(25)  | NO   |     | NULL    |                || officeCode     | int          | NO   | MUL | NULL    |                || jobTitle       | varchar(50)  | NO   |     | NULL    |                || birth          | datetime     | YES  |     | NULL    |                || note           | varchar(255) | YES  |     | NULL    |                || sex            | varchar(5)   | YES  |     | NULL    |                |+----------------+--------------+------+-----+---------+----------------+9 rows in set (0.00 sec)mysql>

6、mysql字段移动

将数据表employees的mobile字段修改到officeCode字段后面；

mysql> alter table employees modify mobile varchar(25) after officeCode;Query OK, 0 rows affected (0.07 sec)Records: 0  Duplicates: 0  Warnings: 0mysql>  desc employees;+----------------+--------------+------+-----+---------+----------------+| Field          | Type         | Null | Key | Default | Extra          |+----------------+--------------+------+-----+---------+----------------+| employeeNumber | int          | NO   | PRI | NULL    | auto_increment || lastname       | varchar(50)  | NO   |     | NULL    |                || firstname      | varchar(50)  | NO   |     | NULL    |                || officeCode     | int          | NO   | MUL | NULL    |                || mobile         | varchar(25)  | YES  |     | NULL    |                || jobTitle       | varchar(50)  | NO   |     | NULL    |                || birth          | datetime     | YES  |     | NULL    |                || note           | varchar(255) | YES  |     | NULL    |                || sex            | varchar(5)   | YES  |     | NULL    |                |+----------------+--------------+------+-----+---------+----------------+9 rows in set (0.00 sec)mysql>

7、mysql字段修改

将数据表employees的birth字段改名为employee_birth；

mysql> alter table employees change birth employee_birth datetime;Query OK, 0 rows affected (0.03 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> desc employees;+----------------+--------------+------+-----+---------+----------------+| Field          | Type         | Null | Key | Default | Extra          |+----------------+--------------+------+-----+---------+----------------+| employeeNumber | int          | NO   | PRI | NULL    | auto_increment || lastname       | varchar(50)  | NO   |     | NULL    |                || firstname      | varchar(50)  | NO   |     | NULL    |                || officeCode     | int          | NO   | MUL | NULL    |                || mobile         | varchar(25)  | YES  |     | NULL    |                || jobTitle       | varchar(50)  | NO   |     | NULL    |                || employee_birth | datetime     | YES  |     | NULL    |                || note           | varchar(255) | YES  |     | NULL    |                || sex            | varchar(5)   | YES  |     | NULL    |                |+----------------+--------------+------+-----+---------+----------------+9 rows in set (0.00 sec)mysql>

8、mysql修改字段类型

将数据表sex字段的数据类型，改成char(1)，非空约束；

mysql> alter table employees modify sex char(1) not null;Query OK, 0 rows affected (0.08 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> desc employees;+----------------+--------------+------+-----+---------+----------------+| Field          | Type         | Null | Key | Default | Extra          |+----------------+--------------+------+-----+---------+----------------+| employeeNumber | int          | NO   | PRI | NULL    | auto_increment || lastname       | varchar(50)  | NO   |     | NULL    |                || firstname      | varchar(50)  | NO   |     | NULL    |                || officeCode     | int          | NO   | MUL | NULL    |                || mobile         | varchar(25)  | YES  |     | NULL    |                || jobTitle       | varchar(50)  | NO   |     | NULL    |                || employee_birth | datetime     | YES  |     | NULL    |                || note           | varchar(255) | YES  |     | NULL    |                || sex            | char(1)      | NO   |     | NULL    |                |+----------------+--------------+------+-----+---------+----------------+9 rows in set (0.00 sec)mysql>

9、mysql删除字段

删除数据表employees中的note字段；

mysql> alter table employees drop note;Query OK, 0 rows affected (0.02 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> desc employees;+----------------+-------------+------+-----+---------+----------------+| Field          | Type        | Null | Key | Default | Extra          |+----------------+-------------+------+-----+---------+----------------+| employeeNumber | int         | NO   | PRI | NULL    | auto_increment || lastname       | varchar(50) | NO   |     | NULL    |                || firstname      | varchar(50) | NO   |     | NULL    |                || officeCode     | int         | NO   | MUL | NULL    |                || mobile         | varchar(25) | YES  |     | NULL    |                || jobTitle       | varchar(50) | NO   |     | NULL    |                || employee_birth | datetime    | YES  |     | NULL    |                || sex            | char(1)     | NO   |     | NULL    |                |+----------------+-------------+------+-----+---------+----------------+8 rows in set (0.00 sec)mysql>

10、mysql增加字段

在数据表employees中新增字段favoriate_activity，并设置数据类型为varchar(100)；

mysql> alter table employees add favoriate_activiry varchar(100);Query OK, 0 rows affected (0.03 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> desc employees;+--------------------+--------------+------+-----+---------+----------------+| Field              | Type         | Null | Key | Default | Extra          |+--------------------+--------------+------+-----+---------+----------------+| employeeNumber     | int          | NO   | PRI | NULL    | auto_increment || lastname           | varchar(50)  | NO   |     | NULL    |                || firstname          | varchar(50)  | NO   |     | NULL    |                || officeCode         | int          | NO   | MUL | NULL    |                || mobile             | varchar(25)  | YES  |     | NULL    |                || jobTitle           | varchar(50)  | NO   |     | NULL    |                || employee_birth     | datetime     | YES  |     | NULL    |                || sex                | char(1)      | NO   |     | NULL    |                || favoriate_activiry | varchar(100) | YES  |     | NULL    |                |+--------------------+--------------+------+-----+---------+----------------+9 rows in set (0.00 sec)mysql>

11、mysql删除表

删除数据表offices；

需要注意的是数据表offices中存在着外键，所以我们删除该数据表的时候，需要先删除外键关系，然后再删除这个数据表方可。

（1）mysql删除外键

先看下外键的名字叫啥；

mysql> show create table employees\G;*************************** 1. row ***************************       Table: employeesCreate Table: CREATE TABLE `employees` (  `employeeNumber` int NOT NULL AUTO_INCREMENT,  `lastname` varchar(50) NOT NULL,  `firstname` varchar(50) NOT NULL,  `officeCode` int NOT NULL,  `mobile` varchar(25) DEFAULT NULL,  `jobTitle` varchar(50) NOT NULL,  `employee_birth` datetime DEFAULT NULL,  `sex` char(1) NOT NULL,  `favoriate_activiry` varchar(100) DEFAULT NULL,  PRIMARY KEY (`employeeNumber`),  KEY `office_fk` (`officeCode`),  CONSTRAINT `office_fk` FOREIGN KEY (`officeCode`) REFERENCES `offices` (`officeCode`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci1 row in set (0.00 sec)ERROR:No query specifiedmysql>

可以看到外键名字是office_fk，然后我们删除employees数据表的外键约束office_fk；

mysql> alter table employees drop foreign key office_fk;Query OK, 0 rows affected (0.02 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> show create table employees\G;*************************** 1. row ***************************       Table: employeesCreate Table: CREATE TABLE `employees` (  `employeeNumber` int NOT NULL AUTO_INCREMENT,  `lastname` varchar(50) NOT NULL,  `firstname` varchar(50) NOT NULL,  `officeCode` int NOT NULL,  `mobile` varchar(25) DEFAULT NULL,  `jobTitle` varchar(50) NOT NULL,  `employee_birth` datetime DEFAULT NULL,  `sex` char(1) NOT NULL,  `favoriate_activiry` varchar(100) DEFAULT NULL,  PRIMARY KEY (`employeeNumber`),  KEY `office_fk` (`officeCode`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci1 row in set (0.00 sec)ERROR:No query specifiedmysql>

可以看到employees数据表中的外键已经删除了，然后我们再返回来删除数据表offices；

（2）mysql删除数据表

mysql> drop table offices;Query OK, 0 rows affected (0.03 sec)mysql> show tables;+-------------------+| Tables_in_company |+-------------------+| employees         |+-------------------+1 row in set (0.00 sec)mysql>

我们删除了数据表之后查询确实只有一个表了。

12、mysql修改存储引擎

将employees数据表的存储引擎修改为myisam；

（1）查看数据表employees现在的存储引擎是什么；

mysql> show create table employees\G;*************************** 1. row ***************************       Table: employeesCreate Table: CREATE TABLE `employees` (  `employeeNumber` int NOT NULL AUTO_INCREMENT,  `lastname` varchar(50) NOT NULL,  `firstname` varchar(50) NOT NULL,  `officeCode` int NOT NULL,  `mobile` varchar(25) DEFAULT NULL,  `jobTitle` varchar(50) NOT NULL,  `employee_birth` datetime DEFAULT NULL,  `sex` char(1) NOT NULL,  `favoriate_activiry` varchar(100) DEFAULT NULL,  PRIMARY KEY (`employeeNumber`),  KEY `office_fk` (`officeCode`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci1 row in set (0.00 sec)ERROR:No query specifiedmysql>

（2）修改数据表的存储引擎；

mysql> alter table employees engine=myisam;Query OK, 0 rows affected (0.06 sec)Records: 0  Duplicates: 0  Warnings: 0mysql>

（3）再次查看数据表的存储引擎；

mysql> show create table employees\G;*************************** 1. row ***************************       Table: employeesCreate Table: CREATE TABLE `employees` (  `employeeNumber` int NOT NULL AUTO_INCREMENT,  `lastname` varchar(50) NOT NULL,  `firstname` varchar(50) NOT NULL,  `officeCode` int NOT NULL,  `mobile` varchar(25) DEFAULT NULL,  `jobTitle` varchar(50) NOT NULL,  `employee_birth` datetime DEFAULT NULL,  `sex` char(1) NOT NULL,  `favoriate_activiry` varchar(100) DEFAULT NULL,  PRIMARY KEY (`employeeNumber`),  KEY `office_fk` (`officeCode`)) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci1 row in set (0.00 sec)ERROR:No query specifiedmysql>

13、mysql修改表名

将数据表employees的数据表名修改成employees_info；

mysql> alter table employees rename employees_info;Query OK, 0 rows affected (0.01 sec)mysql> show tables;+-------------------+| Tables_in_company |+-------------------+| employees_info    |+-------------------+1 row in set (0.00 sec)mysql>

至此，本文结束。

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