[LeetCode] Employees Earning More Than Their Managers 员工挣得比经理多
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 | +----------+
这道题给我们了一个Employee表，里面有员工的薪水信息和其经理的信息，经理也属于员工，其经理Id为空，让我们找出薪水比其经理高的员工，那么就是一个很简单的比较问题了，我们可以生成两个实例对象进行内交通过ManagerId和Id，然后限制条件是一个Salary大于另一个即可：
解法一：
SELECT e1.Name FROM Employee e1 JOIN Employee e2 ON e1.ManagerId = e2.Id WHERE e1.Salary > e2.Salary;
我们也可以不用Join，直接把条件都写到where里也行：
解法二：
SELECT e1.Name FROM Employee e1, Employee e2 WHERE e1.ManagerId = e2.Id AND e1.Salary > e2.Salary;
参考资料：
https://leetcode.com/discuss/88189/two-straightforward-way-using-where-and-join
