MySQL语句练习---由简入繁

创表

1. 设计一张图书表，包含以下字段：图书名称，图书作者、图书价格、图书分类

create table books(
	name varchar(20) comment"图书名称",
	author varchar(10) comment"图书作者",
	price float comment"图书价格",
	classify varchar(10) comment"图书分类"
);

2. 设计一张老师表，包含以下字段：姓名、年龄、身高、体重、性别、学历、生日、身份证号

create table teachers(
	name varchar(10) comment "姓名",
	age int(3) comment "年龄",
	hight float comment "身高",
	weight float comment "体重",
	gender varchar(1) comment "性别",
	education varchar(10) comment "学历",
	birthday datetime comment "生日",
	id varchar(20) comment "身份证号"
);

3. 设计一张商品表，包含以下字段：商品名称、商品价格、商品库存、商品描述

create table commodity(
	name varchar(20) comment "商品名称",
	price float comment "商品价格",
	inventory int comment "商品库存",
	description text comment "商品描述"
);

表的增删改

1. 在图书表中新增一条记录：Java核心技术、作者“Cay S. Horstman”，价格56.43，分类为“计算机技术”

insert into books values("Java核心技术","Cay S. Horstman",53.43,"计算机技术");

2. 修改“Java核心技术”的图书信息，将价格修改为61

update books set price = 61 where name = "java核心技术";

3. 删除商品表中，价格大于60，或者是库存小于200的记录

delete from commodity where price > 60 or inventory < 200;

4. 修改所有库存大于30的商品记录，将价格增加50块

update commodity set price = price+50 where price > 30;

5. 在以上创建的商品表中插入一条数据：名称为“学生书包”、价格18.91、库存101、描述为空

insert into commodity values ("学生书包",18.91,101,null);

6. 查询用户user表中，满足以下条件的用户数据：
   ID在1至200或300至500，且账号accout列不为空
   充值金额amount在1000以上。

create table user(
	id int,
	account varchar(20),
	amount int
);
insert into user values
(1,"523",20),
(250,"600",2000),
(400,null,6000),
(420,"900",5321),
(500,"150",4444),
(200,null,60);

select * from user where ((id between 1 and 200) or (id between 300 and 500)) and account is not null and amount > 1000; 

7. 查询book图书表中，作者author列不为空，或者满足条件：价格price在50元以上且出版日期publish_date在2019年之后的图书信息

create table book(
	name varchar(20),
	author varchar(20),
	price int,
	publish_data datetime
);
insert into book values
("计算机基础","阿星",60,"2020.3.4"),
("操作系统","阿琦",20,"2021.4.4"),
("数据库","阿朵",84,"2009.12.10"),
("java","阿明",18,"2011.8.9"),
("c语言",null,60,"2020.3.4"),
("c语言",null,15,"2021.3.8");

select * from book where author is not null and price > 50 and publish_date > "2019";

8. 查询article文章表中，文章标题title为空，或者满足发表日期create_date在2019年1月1日之后

create table aritcle(
	title varchar(20),
	create_date datetime
);
insert into aritcle values
(null,"2020-03-04"),
("计算机","2021-04-04"),
(null,"2009-12-10"),
("数据库","2011-08-09"),
(null,"2020-03-04");

select * from aritcle where title is null and create_date > "2019.1.1";

9. 查询article文章表中，发表日期create_date在2019年1月1日上午10点30分至2019年11月10日下午4点2分的文章

insert into aritcle values
(null,"2019.1.1 10:53:11"),
(null,"2019.5,6 15:23:55");

select * from aritcle where create_date between "2019.1.1 10:30" and "2019.11.10 4:2";

10. student学生表中，字段有姓名name，年龄age，要求查询姓张，并且年龄在18到25岁之间的学生

create table stu(
	name varchar(20),
	age int
);
insert into stu values
("张雷锋",20),
("樊亦星",21),
("张大炮",50),
("琦琦",23),
("张晓丽",5);

select * from stu where name like "张%" and age between 18 and 25;

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数据库约束、表的设计

1. 学校食堂管理系统，包含食堂表，食堂仓口表，仓口收费记录表

create batadase school_canteen;

use school_canteen;

create table canteen(
	c_id int primary key;
	c_name varchar(20) unique
);

create table hatch(
	h_id int primary key,
	h_name varchar(20),
	foreign key (h_id) references canteen(c_id)
);

create table charge(
	c_id int primary key,
	c_name varchar，
	c_price int,
	foreign key (c_price) references hatch(id)
);

2. 车辆违章系统，包含用户表，车辆表，违章信息表。违章信息表中包含用户和车辆的违章信息

create database car_violation;

use car_violation;

drop table if exists user;
create table user(
	u_id varchar(20) primary key comment "身份证号",
	u_name varchar(20) comment "姓名"
);


drop table if exists car;
create table car(
	c_id varchar(20) primary key comment "车辆编号"
);

create table violation(
	v_userid varchar(20) comment "车主身份证号",
	foreign key (v_userid) references user(u_id),
	v_carid varchar(20) comment "车辆编号",
	foreign key (v_carid) references car(c_id)
);

3. 学校宿舍管理系统，要求包含宿舍信息，学生信息，每日的宿舍查房记录。

create database school_dormitory;

use school_dormitory;

drop table if exists dormitory;
create table dormitory(
	d_id int primary key comment "宿舍号",
	d_college varchar(20) comment "所属学院"
);

drop table if exists student;
create table student(
	s_id varchar(20) primary key comment "学号",
	s_name varchar(20) comment "学生姓名",
	s_dormitory int comment "学生宿舍号",
	foreign key (s_dormitory) references dormitory(d_id)
);

drop table if exists inspect;
create table inspect(
	i_date datetime comment "日期",
	i_dor int comment "宿舍号",
	i_level varchar(5) comment "优良中差",
	foreign key (i_dor) references dormitory(d_id)
);

4. 考勤系统，包含员工表，考勤记录表

create database record;

use record;

drop table if exists staff;
create table staff(
	s_id varchar(20) primary key comment "员工编号",
	s_name varchar(20) comment "员工姓名"
);

drop table if exists attend;
create table attend(
	a_date datetime comment "考勤日期",
	a_staffid varchar(20) comment "员工编号",
	foreign key (a_staffid) references staff(s_id),
	a_time float(3,1) comment "出勤时间"
);

---

合并查询、子查询、联表查询、聚合查询

1. 有一张员工表emp，字段：姓名name，性别sex，部门depart，工资salary。查询以下数据：
   (1)查询男女员工的平均工资
   (2)查询各部门的总薪水
   (3)查询总薪水排名第二的部门
   (4)查询姓名重复的员工信息
   (5)查询各部门薪水大于10000的男性员工的平均薪水

有一张员工表emp，字段：姓名name，性别sex，部门depart，工资salary

use test;

drop table if exists emp;
create table emp(
	name varchar(10) comment "姓名",
	sex varchar(1) comment "性别",
	depart varchar(20) comment "部门",
	salary int comment "工资"
);

insert into emp values
("阿星","男","计算机",56),
("阿奇","女","计算机",66),
("阿甜","女","网络",49),
("阿纳","男","能源",89),
("阿赫","男","会计",46),
("阿辰","女","能源",55),
("阿彪","男","网络",66),
("阿妹","女","计算机",99),
("阿星","男","能源",78);

1、查询男女员工的平均工资
select sex,avg(salary) from emp group by sex;


2、查询各部门的总薪水
select depart,sum(salary) from emp group by depart;


3、查询总薪水排名第二的部门
select depart,sum(salary) from emp group by depart order by sum(salary) desc limit 1,1;


4、查询姓名重复的员工信息
select * from emp where name in(
select name from emp group by name having count(name) > 1);


5、查询各部门薪水大于55的男性员工的平均薪水
select depart,avg(salary) from emp where salary > 55 and sex = "男" group by depart ;

2. 现在有员工表、部门表和薪资表。部门表depart的字段有depart_id， name；员工表 staff 的字段有 staff_id， name， age， depart_id；薪资表salary 的字段有 salary_id，staff_id，salary，month。
   （问题a）：求每个部门’2016-09’月份的部门薪水总额
   （问题b）：求每个部门的部门人数，要求输出部门名称和人数
   （问题c）：求公司每个部门的月支出薪资数，要求输出月份和本月薪资总数

现在有员工表、部门表和薪资表。
部门表depart的字段有depart_id， name；
员工表 staff 的字段有 staff_id， name， age， depart_id；
薪资表salary 的字段有 salary_id，staff_id，salary，month。
create database stafftest;

use stafftest;

drop table if exists depart;
create table depart(
	depart_id int primary key,
	name varchar(20)
);


insert into depart values
(1,"计算机"),
(2,"电控"),
(3,"会计"),
(4,"能源");


drop table if exists staff;
create table staff(
	staff_id int primary key,
	name varchar(20),
	age int,
	depart_id int,
	foreign key (depart_id) references depart(depart_id)
);


insert into staff values
(1,"阿星",18,1),
(2,"阿明",44,1),
(3,"阿珍",5,1),
(4,"阿甜",46,2),
(5,"阿奶",75,2),
(6,"阿彪",26,3),
(7,"阿忠",21,3),
(8,"阿赫",33,4),
(9,"阿阳",22,4);


drop table if exists salary;
create table salary(
	salary_id int,
	staff_id int,
	foreign key (staff_id) references staff(staff_id),
	salary int,
	month datetime
);


insert into salary values
(1,1,56,"2016.9.1"),
(2,2,88,"2016.9.1"),
(3,3,16,"2016.9.1"),
(4,4,78,"2016.9.1"),
(5,5,44,"2016.9.1"),
(6,6,48,"2016.9.1"),
(7,7,75,"2016.9.1"),
(8,8,68,"2016.9.1"),
(9,9,79,"2016.9.1");


（问题a）：求每个部门'2016-09'月份的部门薪水总额
select depart.name,sum(salary.salary)
from staff,salary,depart
where staff.staff_id = salary.staff_id and depart.depart_id = staff.depart_id
group by staff.depart_id;


（问题b）：求每个部门的部门人数，要求输出部门名称和人数
select depart.name,count(staff_id)
from depart,staff
where depart.depart_id = staff.depart_id
group by depart.name;


（问题c）：求公司每个部门的月支出薪资数，要求输出月份和本月薪资总数
select month,sum(salary)
from salary,staff
where salary.staff_id = staff.staff_id
group by depart_id;

3. 有两个表分别如下：
   表A(varchar(32) name， int grade)
   数据：zhangshan 80， lisi 60， wangwu 84
   表B(varchar(32) name， int age)
   数据：zhangshan 26， lisi 24， wangwu 26， wutian 26
   写SQL语句得到如下查询结果：

NAME	GRADE	AGE
zhangshan	80	26
lisi	60	24
wangwu	84	26
wutian	null	26

drop table if exists a;
create table a(
	name varchar(32),
	grade int
);


insert into a values
("zhangshan",80),
("lisi",60),
("wangwu",84);


drop table if exists b;
create table b(
	name varchar(32),
	age int
);


insert into b values
("zhangshan",26),
("lisi",24),
("wangwu",26),
("wutian",26);


select a.name,grade,age
from a right join b
on a.name = b.name;

4. 编写一个SQL查询，获取Employee表中第二高的薪水（Salary）
   ±----±------+
   | Id | Salary|
   ±----±------+
   | 1 | 100 |
   ±----±------+
   | 2 | 200 |
   ±----±------+
   | 3 | 300 |
   ±----±------+
   例如上述Employee表，SQL查询应该返回200作为第二高的薪水。如果不存在第二高的薪水，那么查询应该返回null。
   ±--------------------+
   | SecondHighestSalary |
   ±--------------------+
   | 200 |
   ±--------------------+

drop table if exists salary;
create table salary(
	id int,
	salary int
);


insert into salary values
(1,100),
(2,200),
(3,300);


select salary as SecondHighestSalary
from salary
order by salary desc
limit 1,1;

5. 使用UNION语句查询
   已知T1和T2的字段定义完全相同，T1有5条不同数据，T2有5条不同数据，其中T1有2条数据存在表T2中，使用UNION语句查询这些数据，要求重复数据不出现

select * from t1 union select * from t2;