Duplicate Emails Leetcode SQL

hyperbolechi

于 2015-01-19 02:42:30 发布

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分类专栏： leetcode 文章标签： leetcode SQL

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本文介绍了一种使用SQL自连接的方法来找出Person表中重复的电子邮件地址。通过一个具体的例子展示了如何构造查询语句，返回所有重复出现的电子邮件。

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

+----+---------+
| Id | Email |
+----+---------+
| 1 | a@b.com |
| 2 | c@d.com |
| 3 | a@b.com |
+----+---------+
For example, your query should return the following for the above table:

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

Note: All emails are in lowercase.

这题用self join可以解决

# Write your MySQL query statement below
SELECT DISTINCT a.Email 
FROM Person a JOIN Person b
ON(a.Email=b.Email and a.Id<>b.Id)