题目9：MySQL---------Department Top Three Salaries

The Employee table holds all employees. Every employee has an Id, and there is also a column for the 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            |
+----+-------+--------+--------------+

The Department table holds all departments of the company.

+----+----------+
| Id | Name     |
+----+----------+
| 1  | IT       |
| 2  | Sales    |
+----+----------+

Write a SQL query to find employees who earn the top three salaries in each of the department. For the above tables, your SQL query should return the following rows.

+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Max      | 90000  |
| IT         | Randy    | 85000  |
| IT         | Joe      | 70000  |
| Sales      | Henry    | 80000  |
| Sales      | Sam      | 60000  |
+------------+----------+--------+

create table Employee 
(
  Id int         NOT      NULL AUTO_INCREMENT,
  Name           char(10) null,
  Salary         int      null,
  DepartmentId   int      null,
  primary key (Id)
);

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",9000,1);
INSERT INTO Employee(Id ,Name,Salary,Departmentid) values(5,"Janet",69000,1);
INSERT INTO Employee(Id ,Name,Salary,Departmentid) values(6,"Randy",85000,1);
create table Department
(
  Id    INT      NOT NULL auto_increment,
  Name  char(10) NULL,
  primary key (Id) 
);

insert into Department(Id, Name) values(1,"IT");
insert into Department(Id, Name) values(2,"Sales");

答案：

select D.Name as Department, E.Name as Employee, E.Salary as Salary 
  from Employee E, Department D
   where (select count(distinct(Salary)) from Employee 
           where DepartmentId = E.DepartmentId and Salary > E.Salary) in (0, 1, 2)
         and 
           E.DepartmentId = D.Id 
         order by E.DepartmentId, E.Salary DESC;