数据库（MySQL）练习
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：
sql
mysql -uroot -p #以管理员身份登录
sql
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’***'
sql
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
sql
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)
sql
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:
sql
mysql> show tables;
+-------------------------+
| Tables_in_mydb6_product |
+-------------------------+
| employees |
| invoices |
| orders |
+-------------------------+
3 rows in set (0.01 sec)
1.16练习
准备工作：
sql
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mydb1_test |
| mydb2_stuinfo |
| mydb3_employee |
| mydb4_product |
| mydb5_sales |
| mydb6_product |
| mydb7_openlab |
| mydb_temp1 |
| mydbx_temp3 |
| mysql |
| performance_schema |
| sys |
| temp1 |
+--------------------+
14 rows in set (0.00 sec)
mysql> create database mydb8_work;
Query OK, 1 row affected (0.01 sec)
mysql> use mydb8_work;
Database changed
mysql> select database();
+------------+
| database() |
+------------+
| mydb8_work |
+------------+
1 row in set (0.00 sec)插入数据：
sql
mysql> insert into t_worker values(101,1001,'2015-5-4',7500.00,'群众','张春燕','1990-7
-1');
Query OK, 1 row affected (0.02 sec)
mysql> insert into t_worker values(101,1002,'2019-2-6',5200.00,'团员','李名博','1997-2-8');
Query OK, 1 row affected (0.02 sec)
mysql> insert into t_worker values(102,1003,'2008-1-4',10500.00,'党员','王博涵','1983-
6-8');
Query OK, 1 row affected (0.00 sec)
mysql> insert into t_worker values(102,1004,'2016-10-10',5500.00,'群众','赵小军','1994-9-5');
Query OK, 1 row affected (0.02 sec)
mysql> insert into t_worker values(102,1005,'2014-4-1',8800.00,'党员','钱有财','1992-12-30');
Query OK, 1 row affected (0.01 sec)
mysql> insert into t_worker values(103,1006,'2019-5-5',5500.00,'党员','孙菲菲','1996-9
-2');
Query OK, 1 row affected (0.02 sec)完成查询：
(1)、显示 所有 职工 的基本信息。
sql
mysql> select * from t_worker;
+---------------+-----------+-------------+----------+----------+--------+------------+
| department_id | worker_id | worker_date | wages | politics | name | borth_date |
+---------------+-----------+-------------+----------+----------+--------+------------+
| 101 | 1001 | 2015-05-04 | 7500.00 | 群众 | 张春燕 | 1990-07-01 |
| 101 | 1002 | 2019-02-06 | 5200.00 | 团员 | 李名博 | 1997-02-08 |
| 102 | 1003 | 2008-01-04 | 10500.00 | 党员 | 王博涵 | 1983-06-08 |
| 102 | 1004 | 2016-10-10 | 5500.00 | 群众 | 赵小军 | 1994-09-05 |
| 102 | 1005 | 2014-04-01 | 8800.00 | 党员 | 钱有财 | 1992-12-30 |
| 103 | 1006 | 2019-05-05 | 5500.00 | 党员 | 孙菲菲 | 1996-09-02 |
+---------------+-----------+-------------+----------+----------+--------+------------+
6 rows in set (0.00 sec)(2)、查询所有职工所属部门的部门号，不显示重复的部门号。
去重：distinct
sql
mysql> select * from t_worker;
+---------------+-----------+-------------+----------+----------+--------+------------+
| department_id | worker_id | worker_date | wages | politics | name | borth_date |
+---------------+-----------+-------------+----------+----------+--------+------------+
| 101 | 1001 | 2015-05-04 | 7500.00 | 群众 | 张春燕 | 1990-07-01 |
| 101 | 1002 | 2019-02-06 | 5200.00 | 团员 | 李名博 | 1997-02-08 |
| 102 | 1003 | 2008-01-04 | 10500.00 | 党员 | 王博涵 | 1983-06-08 |
| 102 | 1004 | 2016-10-10 | 5500.00 | 群众 | 赵小军 | 1994-09-05 |
| 102 | 1005 | 2014-04-01 | 8800.00 | 党员 | 钱有财 | 1992-12-30 |
| 103 | 1006 | 2019-05-05 | 5500.00 | 党员 | 孙菲菲 | 1996-09-02 |
+---------------+-----------+-------------+----------+----------+--------+------------+
6 rows in set (0.00 sec)
mysql> select distinct department_id from t_worker;
+---------------+
| department_id |
+---------------+
| 101 |
| 102 |
| 103 |
+---------------+
3 rows in set (0.00 sec)(3)、求出所有职工的人数。
聚合函数 - count（统计数量）
select 聚合函数(字段列表) from 表名
有主键count(worker_id)，不然就用count(1)
sql
mysql> select * from t_worker;
+---------------+-----------+-------------+----------+----------+--------+------------+
| department_id | worker_id | worker_date | wages | politics | name | borth_date |
+---------------+-----------+-------------+----------+----------+--------+------------+
| 101 | 1001 | 2015-05-04 | 7500.00 | 群众 | 张春燕 | 1990-07-01 |
| 101 | 1002 | 2019-02-06 | 5200.00 | 团员 | 李名博 | 1997-02-08 |
| 102 | 1003 | 2008-01-04 | 10500.00 | 党员 | 王博涵 | 1983-06-08 |
| 102 | 1004 | 2016-10-10 | 5500.00 | 群众 | 赵小军 | 1994-09-05 |
| 102 | 1005 | 2014-04-01 | 8800.00 | 党员 | 钱有财 | 1992-12-30 |
| 103 | 1006 | 2019-05-05 | 5500.00 | 党员 | 孙菲菲 | 1996-09-02 |
+---------------+-----------+-------------+----------+----------+--------+------------+
6 rows in set (0.00 sec)
mysql> select count(worker_id) from t_worker;
+------------------+
| count(worker_id) |
+------------------+
| 6 |
+------------------+
1 row in set (0.03 sec)(4)、列出最高工和最低工资。
聚合函数：
sql
mysql> select max(wages) '最高工资' , min(wages)'最低工资' from t_worker;
+----------+----------+
| 最高工资 | 最低工资 |
+----------+----------+
| 10500.00 | 5200.00 |
+----------+----------+
1 row in set (0.00 sec)(5)、列出职工的平均工资和总工资。
sql
mysql> select round(avg(wages),2) '平均工资',sum(wages)'总工资' from t_worker;
+----------+----------+
| 平均工资 | 总工资 |
+----------+----------+
| 7166.67 | 43000.00 |
+----------+----------+
1 row in set (0.01 sec)(6)、创建一个只有职工号、姓名和参加工作的新表，名为工作日期表。
sql
mysql> create table t_workdate select worker_id,name,worker_date from t_worker;
Query OK, 6 rows affected (0.03 sec)
Records: 6 Duplicates: 0 Warnings: 0
mysql> select * from t_workdate;
+-----------+--------+-------------+
| worker_id | name | worker_date |
+-----------+--------+-------------+
| 1001 | 张春燕 | 2015-05-04 |
| 1002 | 李名博 | 2019-02-06 |
| 1003 | 王博涵 | 2008-01-04 |
| 1004 | 赵小军 | 2016-10-10 |
| 1005 | 钱有财 | 2014-04-01 |
| 1006 | 孙菲菲 | 2019-05-05 |
+-----------+--------+-------------+
6 rows in set (0.00 sec)(7)、显示所有党员的年龄。
sql
mysql> select year(now())-year(borth_date) '年龄' from t_worker where politics='党员';
+------+
| 年龄 |
+------+
| 42 |
| 33 |
| 29 |
+------+
3 rows in set (0.01 sec)使表格更加完整：
sql
mysql> select name'姓名',politics'政治面貌',year(now())-year(borth_date) '年龄' from t
_worker where politics='党员';
+--------+----------+------+
| 姓名 | 政治面貌 | 年龄 |
+--------+----------+------+
| 王博涵 | 党员 | 42 |
| 钱有财 | 党员 | 33 |
| 孙菲菲 | 党员 | 29 |
+--------+----------+------+
3 rows in set (0.00 sec)(8)、列出工资在4000-8000之间的所有职工姓名
sql
mysql> select name from t_worker where wages>=4000 and wages<=8000;
+--------+
| name |
+--------+
| 张春燕 |
| 李名博 |
| 赵小军 |
| 孙菲菲 |
+--------+
4 rows in set (0.00 sec)(9)、列出所有孙姓和李姓的职工姓名。
sql
mysql> select name '姓名' from t_worker where name like '孙%' or name like '李%' ;
+--------+
| 姓名 |
+--------+
| 李名博 |
| 孙菲菲 |
+--------+
2 rows in set (0.00 sec)(10)、列出所有部门号为102和103日不是党员的职工号、姓名。
sql
mysql> select worker_id,name from t_worker where (department_id=102 or department_id=103) and politics != '党员';
+-----------+--------+
| worker_id | name |
+-----------+--------+
| 1004 | 赵小军 |
+-----------+--------+
1 row in set (0.00 sec)(11)、将职工表t_worker中的职工按出生的先后顺序排序。
升序：asc(ascend)，默认 降序：desc (descend)
sql
mysql> select * from t_worker order by borth_date;
+---------------+-----------+-------------+----------+----------+--------+------------+
| department_id | worker_id | worker_date | wages | politics | name | borth_date |
+---------------+-----------+-------------+----------+----------+--------+------------+
| 102 | 1003 | 2008-01-04 | 10500.00 | 党员 | 王博涵 | 1983-06-08 |
| 101 | 1001 | 2015-05-04 | 7500.00 | 群众 | 张春燕 | 1990-07-01 |
| 102 | 1005 | 2014-04-01 | 8800.00 | 党员 | 钱有财 | 1992-12-30 |
| 102 | 1004 | 2016-10-10 | 5500.00 | 群众 | 赵小军 | 1994-09-05 |
| 103 | 1006 | 2019-05-05 | 5500.00 | 党员 | 孙菲菲 | 1996-09-02 |
| 101 | 1002 | 2019-02-06 | 5200.00 | 团员 | 李名博 | 1997-02-08 |
+---------------+-----------+-------------+----------+----------+--------+------------+
6 rows in set (0.00 sec)(12)、显示工资最高的前3名职工的职工号和姓名。
分页查询 - limit 记录数 # 从第一条记录开始显示几条记录
sql
mysql> select worker_id,name from t_worker order by wages desc limit 3;
+-----------+--------+
| worker_id | name |
+-----------+--------+
| 1003 | 王博涵 |
| 1005 | 钱有财 |
| 1001 | 张春燕 |
+-----------+--------+
3 rows in set (0.00 sec)(13)、求出各部门党员的人数。
sql
mysql> select department_id '部门号',count(worker_id) '党员人数' from t_worker where p
olitics = '党员' group by department_id;
+--------+----------+
| 部门号 | 党员人数 |
+--------+----------+
| 102 | 2 |
| 103 | 1 |
+--------+----------+
2 rows in set (0.00 sec)(14)、统计各部门的工资和平均工资并保留2位小数
sql
mysql> select department_id '部门号',sum(wages)'部门工资总和'from t_worker group by de
partment_id;
+--------+--------------+
| 部门号 | 部门工资总和 |
+--------+--------------+
| 101 | 12700.00 |
| 102 | 24800.00 |
| 103 | 5500.00 |
+--------+--------------+
3 rows in set (0.00 sec)(15)、列出总人数大于等于3的部门号和总人数。
sql
mysql> select department_id '部门号',count(worker_id)'人数'from t_worker group by depa
rtment_id having count(worker_id)>=3;
+--------+------+
| 部门号 | 人数 |
+--------+------+
| 102 | 3 |
+--------+------+
1 row in set (0.00 sec)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’
sql
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，
sql
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
sql
mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)
sql
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)