181. Employees Earning More Than Their Managers

1. Employees Earning More Than Their Managers
   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 |
+———-+
Answer1:
使用内连接语句——JOIN

SELECT E.Name Employee   FROM Employee E  INNER JOIN Employee M  ON E.ManagerId=M.Id AND E.Salary>M.Salary;  

Answer2:
使用SELECT FROM WHERE语句——WHERE

SELECT E.Name Employee  FROM Employee E ,Employee M  WHERE E.ManagerId=M.Id AND E.Salary>M.Salary; 

* SELECT * FROM table_a, table_b 得到的结果是两个表的笛儿卡积，也就是说SELECT多表查询时，默认是隐式链接，本例子中首先得到的是employee自身链接产生的4x4的表，在此基础上进行的两个附件条件的查询。*