# Description
邮件地址表：
+----+---------+
| Id | Email |
+----+---------+
| 1 | a@b.com |
| 2 | c@d.com |
| 3 | a@b.com |
+----+---------+
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查找重复的邮件地址：
+---------+
| Email |
+---------+
| a@b.com |
+---------+
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# Solution
对 Email 进行分组，如果并使用 COUNT 进行计数统计，结果大于等于 2 的表示 Email 重复。
SELECT
Email
FROM
Person
GROUP BY
Email
HAVING
COUNT( * ) >= 2;
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# SQL Schema
DROP TABLE
IF
EXISTS Person;
CREATE TABLE Person ( Id INT, Email VARCHAR ( 255 ) );
INSERT INTO Person ( Id, Email )
VALUES
( 1, 'a@b.com' ),
( 2, 'c@d.com' ),
( 3, 'a@b.com' );
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