[LeetCode]DepartmentHighestSalary,解題報告

題目

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

The Department table holds all departments of the company.

Write a SQL query to find employees who have the highest salary in each of the departments. For the above tables, Max has the highest salary in the IT department and Henry has the highest salary in the Sales department.

思路

看到這到題目，我首先考慮的是數據庫級聯。具體思路如下：

select e.DepartmentId, MAX(e.Salary) as Salary, d.Name as Department from Employee as e inner join Department as d on e.DepartmentId = d.Id group by e.DepartmentId;

select t.Department as Department, e.Name as Employee, t.Salary as Salary from Employee as e inner join (1-sql生成的表) as t on e.Salary = t.Salary and and e.DepartmentId = t.DepartmentId;

select t.Department as Department, e.Name as Employee, t.Salary as Salary from Employee as e inner join (select e.DepartmentId, MAX(e.Salary) as Salary, d.Name as Department from Employee as e inner join Department as d on e.DepartmentId = d.Id group by e.DepartmentId) as t on e.Salary = t.Salary and e.DepartmentId = t.DepartmentId;