题目：给定 Employee 表，编写一个 SQL 查询，该查询可以获取收入超过他们经理的员工的姓名。在上面的表格中，Joe 是唯一一个收入超过他的经理的员工。
题解：利用左连接或者子查询都可以。
# Write your MySQL query statement below SELECT T1.Name AS Employee FROM Employee T1 left join Employee T2 ON T1.ManagerId = T2.Id WHERE T1.Salary > T2.Salary
题目：编写一个 SQL 查询，查找 Person 表中所有重复的电子邮箱。
题解：利用HAVING进行筛选
# Write your MySQL query statement below SELECT Email FROM Person GROUP BY 1 HAVING COUNT(*)>1
题目：某网站包含两个表，Customers 表和 Orders 表。编写一个 SQL 查询，找出所有从不订购任何东西的客户。
题解：NOT EXISTS
# Write your MySQL query statement below SELECT T.Name Customers FROM Customers T WHERE NOT EXISTS( SELECT Id FROM Orders WHERE CustomerId = T.Id ) ;
原文：https://www.cnblogs.com/pandas-blue/p/14643937.html