Question

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.

Thinking:

  • Method
# Write your MySQL query statement below
select
    Email
from
    Person
group by
    Email
having
    count(*) > 1

二刷

  1. 使用Email字段作为分组的类别，将count()作为聚合函数。 
    # Write your MySQL query statement below
SELECT Email
FROM Person
GROUP BY Email
HAVING  count(*) > 1;