leetcode 182. Duplicate Emails

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182. Duplicate Emails

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Total Accepted: 14498 Total Submissions: 38364 Difficulty: Easy

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.

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# Write your MySQL query statement below
select distinct p1.Email from 
    Person p1,Person p2 
        where p1.Email=p2.Email 
            and p1.Id!=p2.Id

about distinct

SQL SELECT DISTINCT 语句

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本章讲解 SELECT DISTINCT 语句。

SQL SELECT DISTINCT 语句

在表中，可能会包含重复值。这并不成问题，不过，有时您也许希望仅仅列出不同（distinct）的值。

关键词 DISTINCT 用于返回唯一不同的值。

语法：

SELECT DISTINCT 列名称 FROM 表名称

使用 DISTINCT 关键词

如果要从 "Company" 列中选取所有的值，我们需要使用 SELECT 语句：

SELECT Company FROM Orders

"Orders"表：

Company	OrderNumber
IBM	3532
3wschool	2356
Apple	4698
3wschool	6953

结果：

Company

IBM

3wschool

Apple

3wschool

请注意，在结果集中，3wschool 被列出了两次。

如需从 Company" 列中仅选取唯一不同的值，我们需要使用 SELECT DISTINCT 语句：

SELECT DISTINCT Company FROM Orders 

结果：

Company

IBM

3wschool

Apple

现在，在结果集中，"3wschool" 仅被列出了一次。