一、练习

1.15练习

win11安装配置MySQL超详细教程: https://baijiahao.baidu.com/s?id=1786910666566008458&wfr=spider&for=pc

准备工作：

mysql -uroot -p #以管理员身份登录

mysql> select user(); #查看当前登录账户，登录方式
+----------------+
| user()         |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.00 sec)mysql> show databases; #查看当下账户的所有库
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mydb1_test         |
| mydb2_stuinfo      |
| mydb3_employee     |
| mydb4_product      |
| mydb5_sales        |
| mydb_temp1         |
| mysql              |
| performance_schema |
| sys                |
| temp1              |
+--------------------+
11 rows in set (0.00 sec)mysql> create database mydb6_product; #创建新库 mydb6_product
Query OK, 1 row affected (0.02 sec)mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mydb1_test         |
| mydb2_stuinfo      |
| mydb3_employee     |
| mydb4_product      |
| mydb5_sales        |
| mydb6_product      |
| mydb_temp1         |
| mysql              |
| performance_schema |
| sys                |
| temp1              |
+--------------------+
12 rows in set (0.00 sec)
mysql> use mydb6_product; #转换当前登录库
Database changed
mysql> select database(); 
+---------------+
| database()    |
+---------------+
| mydb6_product |
+---------------+
1 row in set (0.00 sec)

employees表：

主键：primary key
不能为空：not null
设置默认值：default’***'

mysql> create table employees(id int primary key , name varchar(50) not null ,age int ,gender varchar(10) not null default'unknown' ,salary float);
Query OK, 0 rows affected (0.04 sec)mysql> desc employees;
+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| id     | int         | NO   | PRI | NULL    |       |
| name   | varchar(50) | NO   |     | NULL    |       |
| age    | int         | YES  |     | NULL    |       |
| gender | varchar(10) | NO   |     | unknown |       |
| salary | float       | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+
5 rows in set (0.02 sec)

orders表

mysql> create table orders(id int primary key , name varchar(100) not null ,price float,
quantity int ,category varchar(50));
Query OK, 0 rows affected (0.03 sec)mysql> desc orders;
+----------+--------------+------+-----+---------+-------+
| Field    | Type         | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| id       | int          | NO   | PRI | NULL    |       |
| name     | varchar(100) | NO   |     | NULL    |       |
| price    | float        | YES  |     | NULL    |       |
| quantity | int          | YES  |     | NULL    |       |
| category | varchar(50)  | YES  |     | NULL    |       |
+----------+--------------+------+-----+---------+-------+
5 rows in set (0.01 sec)

invoices表：

主键自增长：primary key auto_increment
外键关联到orders表的id列：,foreign key(order_id) references orders(id) 注意用逗号分隔后再开始写外键关联
日期型：date
要求数据大于0：check(数据>0)

mysql> create table invoices(number int primary key auto_increment, order_id int ,foreign key(order_id) references orders(id) ,in_date date,total_amount float check(total_amount>0));
Query OK, 0 rows affected (0.03 sec)mysql> desc invoices;
+--------------+-------+------+-----+---------+----------------+
| Field        | Type  | Null | Key | Default | Extra          |
+--------------+-------+------+-----+---------+----------------+
| number       | int   | NO   | PRI | NULL    | auto_increment |
| order_id     | int   | YES  | MUL | NULL    |                |
| in_date      | date  | YES  |     | NULL    |                |
| total_amount | float | YES  |     | NULL    |                |
+--------------+-------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

3张表如下:

mysql> show tables;
+-------------------------+
| Tables_in_mydb6_product |
+-------------------------+
| employees               |
| invoices                |
| orders                  |
+-------------------------+
3 rows in set (0.01 sec)

练习

二、注意事项

2.1 第四天

日期需要以字符串形式添加 eg.‘2000-10-1’

mysql> insert into student2 value(1001 , '李成峰','男','2000-10-1');
Query OK, 1 row affected (0.01 sec)mysql> select * from student2;
+------+--------+------+------------+
| id   | name   | sex  | birthday   |
+------+--------+------+------------+
| 1001 | 李成峰 | 男   | 2000-10-01 |
+------+--------+------+------------+
1 row in set (0.00 sec)

delete一定要带where，

mysql> select * from student2;
+------+--------+------+------------+
| id   | name   | sex  | birthday   |
+------+--------+------+------------+
| 1001 | 李成峰 | 男   | 2000-10-01 |
| 1002 | 薛佳尹 | 女   | 2012-12-12 |
| 1003 | 孙德胜 | 男   | 1998-12-31 |
| 1004 | 凤飞飞 | 女   | 2009-03-15 |
| 1005 | 尹志平 | 男   | 1235-09-01 |
+------+--------+------+------------+
5 rows in set (0.00 sec)mysql> delete from student2 where id=1005; #单条删除
Query OK, 1 row affected (0.02 sec)mysql> select * from student2;
+------+--------+------+------------+
| id   | name   | sex  | birthday   |
+------+--------+------+------------+
| 1001 | 李成峰 | 男   | 2000-10-01 |
| 1002 | 薛佳尹 | 女   | 2012-12-12 |
| 1003 | 孙德胜 | 男   | 1998-12-31 |
| 1004 | 凤飞飞 | 女   | 2009-03-15 |
+------+--------+------+------------+
4 rows in set (0.00 sec)

delete from student2不加where，删除全表内容，表结构还存在
drop 删除包括表结构

删除之前可开启一个事务，方便回溯

mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)

mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)
开启一个事务，方便回溯mysql> delete from student2 ;
Query OK, 4 rows affected (0.00 sec)mysql> select * from student2;
Empty set (0.00 sec)mysql> desc student2;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id       | int         | NO   | PRI | NULL    |       |
| name     | varchar(30) | NO   |     | NULL    |       |
| sex      | char(2)     | YES  |     | 女      |       |
| birthday | date        | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)mysql> rollback;
Query OK, 0 rows affected (0.00 sec)mysql> select * from student2;
+------+--------+------+------------+
| id   | name   | sex  | birthday   |
+------+--------+------+------------+
| 1001 | 李成峰 | 男   | 2000-10-01 |
| 1002 | 薛佳尹 | 女   | 2012-12-12 |
| 1003 | 孙德胜 | 男   | 1998-12-31 |
| 1004 | 凤飞飞 | 女   | 2009-03-15 |
+------+--------+------+------------+
4 rows in set (0.00 sec)