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 |
+----------+这种单表比较条件，一般都是表内进行join操作.
参照此思路，解题如下所示：
# Write your MySQL query statement below
SELECT
a.Name AS Employee
FROM Employee a, Employee b
WHERE
a.ManagerId = b.Id
AND a.Salary > b.Salary; 运行效率在可以接受的范围，此外语句也较为清晰便于维护.
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