Leetcode day3 find duplicate email addresses

182. Find duplicate email

The difficulty is simple

SQL framework

Write a SQL Inquire about , lookup Person All duplicate email addresses in the table .

Example ：

+----+---------+
| Id | Email   |
+----+---------+
| 1  | [email protected] |
| 2  | [email protected] |
| 3  | [email protected] |
+----+---------+

According to the above input , Your query should return the following results ：

+---------+
| Email   |
+---------+
| [email protected] |
+---------+

explain ： All e-mails are in lowercase letters .

Answer key ：

By reading the question, we can know that we can use group query , Judge the total

This question is also relatively simple. I'll put it directly sql Code

select Email
from Person
group by Email
having count(Email)>=2

You need to query the data in groups first , adopt Emali grouping , And then it's conditional count(Email) The number of is greater than or equal to 2 Of , In this way, the results of the query are repeated email.