sql练习

--建表
create table Regions (
Region_id int not null primary key ,
Region_name varchar(25) 
)
go
--国籍
create table Countries(
Country_id int not null primary key,
Country_name varchar(40),
Region_id int
)
go
--地区
create table Location(
Location_id int not null primary key,
Street_address varchar(40),
Postal_code varchar(12),
City varchar(30) not null,
state_province varchar(25),
country_id char(2)
)
go
--部门
create table Departments(
Department_id int primary key not null,
Department_name varchar(30) not null,
Manager_id int,
Location_id int
)
go
--工资
create table Jobs(
Job_id int primary key not null,
Job_title varchar(35) not null,
Min_salary int ,
Max_salary int
)
--员工
create table Employees(
Employee_id int primary key not null,
First_name varchar(20),
Last_name varchar(25) not null,
Email varchar(25) not null,
Phone_number varchar(20),
Hire_date date not null,
Job_id varchar not null,
Salary numeric(5,2),
Commission_pct numeric(2,2),
Manager_id int,
Department_id int
)


--1. 各个部门平均、最大、最小工资、人数，按照部门号升序排列。
     select  Departments.Department_name as ‘部门‘, 
     avg(salary)as ‘平均工资‘ ,
     max(salary)as ‘最大工资‘,
     min(salary)as ‘最小工资‘,
     count(Employee_id)as ‘人数‘
     from Employees inner join  Departments  
             on  Departments.Department_id = Employees.Department_id
     group by Departments.Department_name ,Departments.Department_id 
     order by  Departments.Department_id asc

--2. 各个部门中工资大于5000的员工人数。
     select Departments.Department_name as ‘部门‘,
     count(*) as ‘人数‘ from Employees 
     inner join  Departments  
             on  Departments.Department_id = Employees.Department_id  
             where Employees.Salary>5000
     group by Departments.Department_name   

--3. 各个部门平均工资和人数，按照部门名字升序排列。
     select Departments.Department_name as ‘部门‘,
     avg(Salary)as ‘平均工资‘ ,
     count(*) as ‘人数‘ from Employees 
     inner join  Departments 
              on Departments.Department_id = Employees.Department_id
     group by Departments.Department_name ,Departments.Department_id 
     order by  Departments.Department_name asc

-- （问题4） 4. 列出每个部门中有同样工资的员工的统计信息，列出他们的部门号，工资，人数。
   （错）  select Employees1.Department_id as ‘部门号‘,
            Employees1.Salary as ‘工资‘,
            COUNT(1) as ‘人数‘ 
            from Employees Employees1,Employees Employeess2 
    　　 where Employees1.Department_id =Employeess2.Department_id
           and Employees1.Salary=Employeess2.Salary 
    　　 group by Employees1.Department_id,Employees1.Salary

    （正） SELECT COUNT(1) AS ‘COUNT‘,
    　　DEPARTMENT_ID,
    　　SALARY
　　FROM EMPLOYEES
　　　GROUP BY DEPARTMENT_ID,SALARY 
　　　HAVING COUNT(1)>1

--（不知道）5. 列出同部门中工资高于1000 的员工数量超过2 人的部门，显示部门名字、地区名称。
      select employee.Department_id as ‘部门号‘,
             department.Department_name as ‘部门‘,
              location1.City as‘地区‘
      from Employees employee,Departments department,Location location1 
      where department.Department_id = employee.Department_id 
      and employee.Salary>1000
      group by department.Department_name,
      employee.Department_id
      --location1.City 
      having count(1)>=2
      order by employee.Department_id

--6. 哪些员工的工资，高于整个公司的平均工资，列出员工的名字和工资（降序）。
     select e.First_name as ‘名字1‘,
       e.Last_name as ‘名字2‘,
       e.Salary as ‘工资‘
     from Employees e
     where e.Salary> (select avg(Employees.Salary)from Employees)
     order by e.Salary desc

--7. 哪些员工的工资，介于1号 和3号部门平均工资之间。
     select e.Department_id as‘ID‘,
       e.First_name as ‘名字1‘,
       e.Last_name as ‘名字2‘,
       e.Salary as ‘工资‘
     from Employees e 
     where e.Salary  between (select avg(Employees.Salary)from Employees where Employees.Department_id =1)
         and (select avg(Employees.Salary)from Employees where Employees.Department_id =3)

-- 8. 所在部门平均工资高于5000 的员工名字。
     select Employees1.Department_id as‘部门号‘,
            Employees1.First_name as‘名字1‘,
            Employees1.Last_name as‘名字2‘,
            Employees1.Salary as ‘工资‘
            from Employees Employees1
            where  
            (select avg(Employees.Salary)from Employees 
            where Employees1.Department_id =Employees.Department_id)>5000

--9. 列出各个部门中工资最高的员工的信息：名字、部门号、工资。
     select e1.First_name as‘名字1‘,
            e1.Last_name as‘名字2‘,
            e1.Department_id as‘部门号‘,
            e1.Salary as‘工资‘
       from Employees e1
           where e1.Salary = (
           select max(Employees.Salary) from
           Employees where e1.Department_id =Employees.Department_id)
           order by e1.Department_id

--(有问题)10. 最高的部门平均工资是多少。
  （错）    select e1.Department_id as‘部门号‘,
             max(e1.Salary) as‘工资‘
             from Employees e1
             where e1.Salary =(select avg(Employees.Salary) from Employees
                  where e1.Department_id = Employees.Department_id)
             group by e1.Department_id  



             --(有问题)10. 平均工资是最高的部门的工资是多少。
  （正）   select top 1 Salary 
         from (
          select 
                a.Department_id as ‘Department_id‘,
             avg(a.Salary) as ‘Salary‘
          from Employees a
             group by a.Department_id ) as b
        order by Salary desc
        


      --求平均值


       select avg(Employees.Salary) from Employees e1,Employees
                   where e1.Department_id= Employees.Department_id
                   group by e1.Department_id