## 题目
编写一个 SQL 查询，查找 Person 表中所有重复的电子邮箱。
示例：
```
+----+---------+
| Id | Email   |
+----+---------+
| 1  | a@b.com |
| 2  | c@d.com |
| 3  | a@b.com |
+----+---------+
```
根据以上输入，你的查询应返回以下结果：

```
+---------+
| Email   |
+---------+
| a@b.com |
+---------+
```

## 答案
```sql
select Email from Person  group by Email having count(*) > 1
```