码疯窝

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      |
+----------+

分析: 此题要注意, 如果是与NULL 比较返回的永远是NULL, 如果一定要比较就要先把NULL 用IF转化一下.

SELECT t.Name FROM Employee t
LEFT JOIN Employee t2
ON t.ManagerId = t2.Id
WHERE t.Salary > t2.Salary
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