leetcode Database2

一、Duplicate Emails

Write a SQL query to find all duplicate emails in a table named Person.

+----+---------+
| Id | Email   |
+----+---------+
| 1  | [email protected] |
| 2  | [email protected] |
| 3  | [email protected] |
+----+---------+

For example, your query should return the following for the above table:

+---------+
| Email   |
+---------+
| [email protected] |
+---------+

Note: All emails are in lowercase.

分析：编写一个SQL查询从Person表中找出所有重复的邮箱地址。

解法一：（self join）

# Write your MySQL query statement below
select distinct a.Email from Person a, Person b where a.Email=b.Email and a.Id<>b.Id

一开始，写的时候没注意把distinct给漏了，导致出错：

Submission Result: Wrong AnswerMore Details

Input:{"headers": {"Person": ["Id", "Email"]}, "rows": {"Person": [[1, "[email protected]"], [2, "[email protected]"]]}}

Output:{"headers": ["Email"], "values": [["[email protected]"], ["[email protected]"]]}

Expected:{"headers": ["Email"], "values": [["[email protected]"]]}　

解法二：

# Write your MySQL query statement below
Select Email
From Person
GROUP BY Email
Having count(Email)>1