第12次课程作业

sql作业.txt

+创建表:
+创建表:
+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', '70000', '1');
+insert into Employee (Id, Name, Salary,DepartmentId) values ('2', 'Henry', '80000', '2');
+insert into Employee (Id, Name, Salary,DepartmentId) values ('3', 'Sam', '60000', '2');
+insert into Employee (Id, Name, Salary,DepartmentId) values ('4', 'Max', '90000', '1');
+insert into Employee (Id, Name, Salary,DepartmentId) values ('5', 'Randy', '85000', '1');
+Truncate table Department;
+insert into Department (Id, Name) values('1', 'IT');
+insert into Department (Id, Name) values('2', 'Sales');
+
+部门工资前三高的员工
+
+Employee 表包含所有员工信息，每个员工有其对应的 Id, salary 和 department Id 。
++----+-------+--------+--------------+
+| Id | Name  | Salary | DepartmentId |
++----+-------+--------+--------------+
+| 1  | Joe   | 70000  | 1            |
+| 2  | Henry | 80000  | 2            |
+| 3  | Sam   | 60000  | 2            |
+| 4  | Max   | 90000  | 1            |
+| 5  | Janet | 69000  | 1            |
+| 6  | Randy | 85000  | 1            |
++----+-------+--------+--------------+
+
+Department 表包含公司所有部门的信息。
++----+----------+
+| Id | Name     |
++----+----------+
+| 1  | IT       |
+| 2  | Sales    |
++----+----------+
+
+编写一个 SQL 查询，找出每个部门工资前三高的员工。例如，根据上述给定的表格，查询结果应返回：
++------------+----------+--------+
+| Department | Employee | Salary |
++------------+----------+--------+
+| IT         | Max      | 90000  |
+| IT         | Randy    | 85000  |
+| IT         | Joe      | 70000  |
+| Sales      | Henry    | 80000  |
+| Sales      | Sam      | 60000  |
++------------+----------+--------+
+
+
+select * from Department d,Employee e where d.Id = e.Department and e.Salary = (select max(Salary) from Employee where DepartmentId = d.Id);
+select d.Name as Department,e.Name as Employee,e.Salary from Department d join Employee e on e.DepartmentId = d.Id where (e,Department,e.Saraly) in (select DepartmentId,max(Saraly) from Employee group by DepartmentId );
+
+答案:
+    SELECT Department.Name AS Department, e1.Name AS Employee, e1.Salary AS Salary
+    FROM Employee e1
+    JOIN Department
+    ON e1.DepartmentId = Department.Id
+    WHERE 3 >   (
+                SELECT COUNT(DISTINCT e2.Salary) 
+                FROM Employee e2
+                WHERE e2.Salary > e1.Salary AND e1.DepartmentId = e2.DepartmentId
+                )
+    ORDER BY Department.Name, e1.Salary DESC
+
+select * from Employee e1 inner join Department d on e1.DepartmentId = d.Id 
+where 3 > (select count(distinct e2.Employee) from Employee e2 where e2.Salary > e1.Salary and e1.DepartmentId = e2.DepartmentId ) group by d.Name,e1.order by desc;
+解析:
+    不妨假设e1=e2=[6,5,4,3]，则子查询的过程如下：
+
+    1、e1.Salary=3；则e2.Salary可以取4、5、6；COUNT(DISTINCT e2.Salary)=3
+    
+    2、e1.Salary=4；则e2.Salary可以取5、6；COUNT(DISTINCT e2.Salary)=2
+    
+    3、e1.Salary=5；则e2.Salary可以取6；COUNT(DISTINCT e2.Salary)=1
+    
+    4、e1.Salary=6；则e2.Salary无法取值；COUNT(DISTINCT e2.Salary)=0
+    
+    则要令COUNT(DISTINCT e2.Salary)  < 3 的情况有上述的4、3、2.
+    
+    也即是说，这等价于取e1.Salary最大的三个值。
+
+部门工资最高的员工:
+    方法1:
+        select d.Name as Department,e.Name as Employee,e.Salary
+        from Department d,Employee e
+        where e.DepartmentId=d.Id and 
+        e.Salary=(Select max(Salary) from Employee where DepartmentId=d.Id)
+    方法2:
+        select d.Name as Department,e.Name as Employee,Salary 
+        from Employee e join Department d on e.DepartmentId=d.Id 
+        where (e.Salary,e.DepartmentId) in (select max(Salary),DepartmentId from Employee group by DepartmentId) 
+
+
+
+