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leetcode-cn/problem (Chinese)/查找重复的电子邮箱 [duplicate-emails].html
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<p>编写一个 SQL 查询，查找&nbsp;<code>Person</code> 表中所有重复的电子邮箱。</p>
<p><meta charset="UTF-8" /></p>
<p><strong>示例：</strong></p>
<p>表:&nbsp;<code>Person</code></p>
<pre>+----+---------+
| Id | Email |
<pre>
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| id | int |
| email | varchar |
+-------------+---------+
id 是该表的主键（具有唯一值的列）。
此表的每一行都包含一封电子邮件。电子邮件不包含大写字母。
</pre>
<p>&nbsp;</p>
<p>编写解决方案来报告所有重复的电子邮件。 请注意，可以保证电子邮件字段不为 NULL。</p>
<p>以&nbsp;<strong>任意顺序&nbsp;</strong>返回结果表。</p>
<p>结果格式如下例。</p>
<p>&nbsp;</p>
<p><strong>示例&nbsp;1:</strong></p>
<pre>
<strong>输入:</strong>
Person 表:
+----+---------+
| id | email |
+----+---------+
| 1 | a@b.com |
| 2 | c@d.com |
| 3 | a@b.com |
+----+---------+
</pre>
<p>根据以上输入，你的查询应返回以下结果：</p>
<pre>+---------+
<strong>输出:</strong>
+---------+
| Email |
+---------+
| a@b.com |
+---------+
</pre>
<p><strong>说明：</strong>所有电子邮箱都是小写字母。</p>
<strong>解释:</strong> a@b.com 出现了两次。</pre>