Employees Earning More Than Their Managers
Created: September 12, 2018 by [lek-tin]
Last updated: March 2, 2020
# SQL Schema:
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', 'None')
insert into Employee (Id, Name, Salary, ManagerId) values ('4', 'Max', '90000', 'None')
The Employee table holds all employees including their managers. Every employee has an Id, and there is also a column for the manager Id.
+----+-------+--------+-----------+
| Id | Name | Salary | ManagerId |
+----+-------+--------+-----------+
| 1 | Joe | 70000 | 3 |
| 2 | Henry | 80000 | 4 |
| 3 | Sam | 60000 | NULL |
| 4 | Max | 90000 | NULL |
+----+-------+--------+-----------+
Given the Employee table, write a SQL query that finds out employees who earn more than their managers. For the above table, Joe is the only employee who earns more than his manager.
+----------+
| Employee |
+----------+
| Joe |
+----------+
Solution (where)
WHERE: Select from two tables will get the Cartesian product of these two tables. In this case, the output will be 4*4 = 16 records. However, what we interest is the employee’s salary higher than his/her manager. So we should add two conditions in a WHERE clause like below.
SELECT
a.Name AS 'Employee'
FROM
Employee AS a,
Employee AS b
WHERE
a.ManagerId = b.Id AND a.Salary > b.Salary
Solution (join)
more efficient than using where
SELECT
a.NAME AS Employee
FROM
Employee AS a
JOIN
Employee AS b
ON a.ManagerId = b.Id
AND a.Salary > b.Salary