SQL -3

4.从不订购的客户

需求：某网站包含两个表,Customers表和Orders表，编写SQL查询，找出所有从不订购商品的客户。

展示效果：

Customers

Henry

Max

建表语句：

Create table If Not Exists Customers (Id int, Name varchar(255));
Create table If Not Exists Orders (Id int, CustomerId int);
Truncate table Customers;
insert into Customers (Id, Name) values (1, 'Joe');
insert into Customers (Id, Name) values (2, 'Henry');
insert into Customers (Id, Name) values (3, 'Sam');
insert into Customers (Id, Name) values (4, 'Max');
Truncate table Orders;
insert into Orders (Id, CustomerId) values (1, 3);
insert into Orders (Id, CustomerId) values (2, 1);

方法1:

select 
	c.name as `customer`
from Customers
where c.id not in (select customerid from Orders);

方法2：

select 
	c.name as `customer`
from Customers c
left join 
	Orders o 
on c.id = o.Customerid 
where o.id is null ;  --  或者 custmerid is null 

5.部门工资最高的员工

需求1：编写一个 SQL 查询，找出每个部门工资最高的员工。例如，根据上述给定的表格，Max 在 IT 部门有最高工资，Henry 在 Sales 部门有最高工资。

效果展示：

Department	Employee	Salary
IT	Jim	90000
IT	Max	90000
Sales	Henry	80000

建表语句：

Create table If Not Exists Employee (Id int, Name varchar(255), Salary int, DepartmentId int);
Create table If Not Exists Department (Id int, Name varchar(255));
Truncate table Employee;
insert into Employee (Id, Name, Salary, DepartmentId) values (1, 'Joe', 75000, 1);
insert into Employee (Id, Name, Salary, DepartmentId) values (2, 'Jim', 90000, 1);
insert into Employee (Id, Name, Salary, DepartmentId) values (3, 'Henry', 80000, 2);
insert into Employee (Id, Name, Salary, DepartmentId) values (4, 'Sam', 60000, 2);
insert into Employee (Id, Name, Salary, DepartmentId) values (5, 'Max', 90000, 1);
insert into Employee (Id, Name, Salary, DepartmentId) values (6, 'Randy', 85000, 1);
insert into Employee (Id, Name, Salary, DepartmentId) values (7, 'Will', 70000, 1);
Truncate table Department;
insert into Department (Id, Name) values (1, 'IT');
insert into Department (Id, Name) values (2, 'Sales');

方法1：

select 
	d.name as 'department',
	e.name as 'employee',
	Salary
from 
	Employee as e 
join 
	Department d
on
	e.departmentid = d.id 
where 
	(e.department,Salary ) in 
	(select 
     	department ,
     	max(salary)
     from department 
     group by departmentid 
    );

方法2：

select 
	department ,employee, salary
from (
	select 
    	d.name as 'department',
    	e.name as 'employee',
    	e.salary,
    	rank() over(partition by d.id order by salary desc ) rk 
    from
    	employee e
    join 
    	department d
    on e.demartmentid = d.id
) t1
where rk = 1;

需求2：找出每个部门获得前三高工资的所有员工。

展示效果：

Department	Employee	Salary
IT	Max	90000
IT	Jim	90000
IT	Randy	85000
IT	Joe	75000
Sales	Henry	80000
Sales	Sam	60000

方法1：

select 
	d.name as 'department',
	e.name as 'employee',
	e1.salary
from
	employee e1
join 
	department d
on
	e1.departmentid = d.id
where 
	(select 
    	distinct count(e2.salary)
    from 
    	employee e2 
    where 
    	e1.salary < e2.salary
    and 
    	e1.deparmentid = e2.departmentid) < 3
order by department,e1.salary desc;    	

方法2：

select 
	department,
	emplyee,
	salary
from 
	(
        select
        	d.name as 'department',
        	e.name as 'employee',
        	e.salary,
        	dense_rank() over(partition by d.id order by salary desc ) rk
        from 
        	employee e
        join  
        	department d
        on
        	e.departmentid = d.id 
    )t1
where rk <= 3;

6.超过经理收入的员工

需求：Employee 表包含所有员工，他们的经理也属于员工。每个员工都有一个 Id，此外还有一列对应员工的经理的 Id。编写一个 SQL 查询，该查询可以获取收入超过他们经理的员工的姓名。

效果展示：

Employee

Joe

建表语句：

create table If Not Exists Employee (Id int, Name varchar(255), Salary int, ManagerId int);
truncate table Employee;
insert into Employee (Id, Name, Salary, ManagerId) values (1, 'Joe', 70000, 3);
insert into Employee (Id, Name, Salary, ManagerId) values (2, 'Henry', 80000, 4);
insert into Employee (Id, Name, Salary, ManagerId) values (3, 'Sam', 60000, null);
insert into Employee (Id, Name, Salary, ManagerId) values (4, 'Max', 90000, null);

方法：

select
	e1.name as 'employee'
from 
	employee e1
join 
	emplyee e2
on 
	e1.managerid = e2.id 
where e1.salary > e2.salary