摘要：
难度：中等表Employee保存了所有的员工数据。+----+-------+--------+--------------+| Id | Name | Salary | DepartmentId |+----+-------+--------+--------------+| 1 | Joe ... 阅读全文
摘要：
难度：容易写一段SQL，在表Person中查找所有重复的Email地址。+----+---------+| Id | Email |+----+---------+| 1 | a@b.com || 2 | c@d.com || 3 | a@b.com |+----+---------+例如... 阅读全文