练习1：数据表的基本操作
已经学习了MySQL的各种操作，如创建表、添加各种约束、产看表结构、以及修改和删除表。给出一个实战演练，全面复习一下数据表的基本操作基础。
案例:创建数据库company，按照下面两个表给出的表结构在company数据库中创建两个数据表offices和employees，按照操作过程完成数据表的基本操作。
操作过程如下：
(1)：登录MySQL。
mysql -h localhost -u root -p
打开windows命令行，输入登录用户名和密码：
C:\Users\Hudie>mysql -h localhost -u root -p
Enter password: ********
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 19
Server version: 8.0.16 MySQL Community Server - GPL
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
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.
mysql>_
登录成功，可以输入SQL语句进行操作。
(2)：创建数据库company。
create database company;
mysql> create database company;
Query OK, 1 row affected (0.06 sec)
创建成功后，在company数据库中创建数据表，必须先选择该数据库。SQL语句如下：
mysql> use company;
Database changed
(3):创建表offices。
create table offices
mysql> create table offices
-> (
-> officeCode int(10) 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 (0.14 sec)
mysql> show tables;
+-------------------+
| Tables_in_company |
+-------------------+
| offices |
+-------------------+
1 row in set (0.00 sec)
(4)：创建表enployees。
create table employees
mysql> create table employees
-> (
-> employeeNumber int(11) not null primary key auto_increment,
-> lastNamee varchar(50) not null,
-> firstName varchar(50) not null,
-> mobile varchar(25) not null,
-> officeCode int (10) not null,
-> jobTitle varchar(50) not null,
-> birth datetime,
-> noth varchar(25),
-> sex varchar(5),
-> constraint office_fk foreign key(officeCode) references offices(officeCode)
-> );
Query OK, 0 rows affected (0.14 sec)
mysql> show tables;
+-------------------+
| Tables_in_company |
+-------------------+
| employees |
| offices |
+-------------------+
2 rows in set (0.01 sec)
创建成功，查看两个表的结构:
mysql> desc offices;
+------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+-------+
| officeCode | int(10) | 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 (0.06 sec)
mysql> desc employees;
+----------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------------+-------------+------+-----+---------+----------------+
| employeeNumber | int(11) | NO | PRI | NULL | auto_increment |
| lastNamee | varchar(50) | NO | | NULL | |
| firstName | varchar(50) | NO | | NULL | |
| mobile | varchar(25) | NO | | NULL | |
| officeCode | int(10) | NO | MUL | NULL | |
| jobTitle | varchar(50) | NO | | NULL | |
| birth | datetime | YES | | NULL | |
| noth | varchar(25) | YES | | NULL | |
| sex | varchar(5) | YES | | NULL | |
+----------------+-------------+------+-----+---------+----------------+
9 rows in set (0.01 sec)
(5)：将表employees的mobile字段修改到officeCode字段后面。
alter table employees modify mobile varchar(25) after officeCode;
mysql> alter table employees modify mobile varchar(25) after officeCode;
Query OK, 0 rows affected (0.18 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc employees;
+----------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------------+-------------+------+-----+---------+----------------+
| employeeNumber | int(11) | NO | PRI | NULL | auto_increment |
| lastNamee | varchar(50) | NO | | NULL | |
| firstName | varchar(50) | NO | | NULL | |
| officeCode | int(10) | NO | MUL | NULL | |
| mobile | varchar(25) | YES | | NULL | |
| jobTitle | varchar(50) | NO | | NULL | |
| birth | datetime | YES | | NULL | |
| noth | varchar(25) | YES | | NULL | |
| sex | varchar(5) | YES | | NULL | |
+----------------+-------------+------+-----+---------+----------------+
9 rows in set (0.01 sec)
(6)：将表employees的birth字段改名为employee_birth。
alter table employees change birth employee_birth datetime;
mysql> alter table employees change birth employee_birth datetime;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc employees;
+----------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------------+-------------+------+-----+---------+----------------+
| employeeNumber | int(11) | NO | PRI | NULL | auto_increment |
| lastNamee | varchar(50) | NO | | NULL | |
| firstName | varchar(50) | NO | | NULL | |
| officeCode | int(10) | NO | MUL | NULL | |
| mobile | varchar(25) | YES | | NULL | |
| jobTitle | varchar(50) | NO | | NULL | |
| employee_birth | datetime | YES | | NULL | |
| noth | varchar(25) | YES | | NULL | |
| sex | varchar(5) | YES | | NULL | |
+----------------+-------------+------+-----+---------+----------------+
9 rows in set (0.00 sec)
(7)：修改sex字段，设置数据类型为char(1),非空约束。
alter table employees modify sex char(1) not null;
mysql> alter table employees modify sex char(1) not null;
Query OK, 0 rows affected (0.20 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc employees;
+----------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------------+-------------+------+-----+---------+----------------+
| employeeNumber | int(11) | NO | PRI | NULL | auto_increment |
| lastNamee | varchar(50) | NO | | NULL | |
| firstName | varchar(50) | NO | | NULL | |
| officeCode | int(10) | NO | MUL | NULL | |
| mobile | varchar(25) | YES | | NULL | |
| jobTitle | varchar(50) | NO | | NULL | |
| employee_birth | datetime | YES | | NULL | |
| noth | varchar(25) | YES | | NULL | |
| sex | char(1) | NO | | NULL | |
+----------------+-------------+------+-----+---------+----------------+
9 rows in set (0.01 sec)
(8)：删除字段noth。
alter table employees drop noth;
mysql> alter table employees drop noth;
Query OK, 0 rows affected (0.15 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc employees;
+----------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------------+-------------+------+-----+---------+----------------+
| employeeNumber | int(11) | NO | PRI | NULL | auto_increment |
| lastNamee | varchar(50) | NO | | NULL | |
| firstName | varchar(50) | NO | | NULL | |
| officeCode | int(10) | 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 (0.01 sec)
(9):增加字段名favoriate_activity,数据类型为varchar(100)
alter table employees add favoriate_activity varchar(100);
mysql> alter table employees add favoriate_activity varchar(100);
Query OK, 0 rows affected (0.09 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc employees;
+--------------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------------+--------------+------+-----+---------+----------------+
| employeeNumber | int(11) | NO | PRI | NULL | auto_increment |
| lastNamee | varchar(50) | NO | | NULL | |
| firstName | varchar(50) | NO | | NULL | |
| officeCode | int(10) | NO | MUL | NULL | |
| mobile | varchar(25) | YES | | NULL | |
| jobTitle | varchar(50) | NO | | NULL | |
| employee_birth | datetime | YES | | NULL | |
| sex | char(1) | NO | | NULL | |
| favoriate_activity | varchar(100) | YES | | NULL | |
+--------------------+--------------+------+-----+---------+----------------+
9 rows in set (0.00 sec)
(10):删除主表offices
①删除表的外键约束:alter table employees drop foreign key office_fk;
②删除表offices:drop table offices;
mysql> alter table employees drop foreign key office_fk;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> drop table offices;
Query OK, 0 rows affected (0.03 sec)
mysql> show tables;
+-------------------+
| Tables_in_company |
+-------------------+
| employees |
+-------------------+
1 row in set (0.06 sec)
(11)修改表employees存储引擎为MyISAM。
alter table employees ENGINE=MyISAM;
mysql> alter table employees ENGINE=MyISAM;
Query OK, 0 rows affected (0.17 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show create table employees \G
*************************** 1. row ***************************
Table: employees
Create Table: CREATE TABLE `employees` (
`employeeNumber` int(11) NOT NULL AUTO_INCREMENT,
`lastNamee` varchar(50) NOT NULL,
`firstName` varchar(50) NOT NULL,
`officeCode` int(10) NOT NULL,
`mobile` varchar(25) DEFAULT NULL,
`jobTitle` varchar(50) NOT NULL,
`employee_birth` datetime DEFAULT NULL,
`sex` char(1) NOT NULL,
`favoriate_activity` varchar(100) DEFAULT NULL,
PRIMARY KEY (`employeeNumber`),
KEY `office_fk` (`officeCode`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
(12)将表employees名称修改为employees_info。
alter table employees rename employees_info;
mysql> alter table employees rename employees_info;
Query OK, 0 rows affected (0.07 sec)
mysql> show tables;
+-------------------+
| Tables_in_company |
+-------------------+
| employees_info |
+-------------------+
1 row in set (0.00 sec)