LeetCode刷题之旅【数据库篇-5】 - 中等： 部门工资最高的员工

2019年11月18日

目录

​​题目 部门工资最高的员工​​

​​解题1​​

​​解题2​​

​​解题3​​

题目 部门工资最高的员工

解题1

• 使用中间表，根据departmentId来group by分组
• 两张表department和employee联表查询后，使用中间表作为where过滤条件

SELECT 
  Department.name AS 'Department',
  Employee.name AS 'Employee',
  Salary
 FROM employee 
join department 
on department.id = employee.DepartmentId
WHERE (employee.DepartmentId,employee.Salary) in (SELECT
    DepartmentId, MAX(Salary)
FROM
    Employee
GROUP BY DepartmentId);

解题2

WHERE内连接 效率与官方题解相近

SELECT
    b.Name AS Department,
    a.Name AS Employee,
    c.Max_Salary AS Salary
FROM 
    Employee AS a,
    Department AS b,
    (
        SELECT DISTINCT DepartmentId, MAX(Salary) AS Max_Salary
        FROM Employee
        GROUP BY DepartmentId
    ) AS c
WHERE a.DepartmentId = c.DepartmentId
    AND a.DepartmentId = b.Id
    AND a.Salary = c.Max_Salary
;

解题3

-- JOIN内连接 效率最低
SELECT 
  b.`Name` as Department,
  a.`Name` as Employee,
  c.Max_Salary as Salary
FROM employee as a 
join (SELECT DISTINCT DepartmentId,MAX(Salary) AS Max_Salary FROM employee GROUP BY DepartmentId) as c 
on a.DepartmentId = c.DepartmentId and a.Salary = c.Max_Salary
JOIN department as b
on a.DepartmentId = b.Id
;