Leetcode Day5 delete duplicate email

196. Delete duplicate email

The difficulty is simple

Write a SQL Inquire about , To delete Person All duplicate email addresses in the table , The duplicate mailbox only keeps Id Minimum the .

±—±-----------------+
| Id | Email |
±—±-----------------+
| 1 | [email protected] |
| 2 | [email protected] |
| 3 | [email protected] |
±—±-----------------+
Id It's the primary key of this table .
for example , After running your query , above Person The table should return the following lines :

±—±-----------------+
| Id | Email |
±—±-----------------+
| 1 | [email protected] |
| 2 | [email protected] |
±—±-----------------+

Tips ：

perform SQL after , The output is the whole Person surface .
Use delete sentence .

Answer key ：

It is not difficult for us to see from the meaning of the title , This question needs to use delete Statement to delete duplicate Email value , Here we can disassemble the subject , First, repeat Email Find out , Then find out Email Delete the result .

1、 Find duplicate Email result

​ The implementation here is to realize query repetition through self table connection Email, The connection condition is a.Email be equal to b.Email, After connection query , We need to judge ourselves in terms of conditions Email Equal rows are deleted , What you get in this way is repetition Email.

select a.*
from Person a
left join Person b
on a.Email = b.Email
where a.Id > b.Id

The operation results are shown in the following table ：

id	Email
3	[email protected]

2、 Delete the queried data

​ All we need to do here is select Replace statement with delete Sentence can be used

sql Code

delete a.*
from Person a
left join Person b
on a.Email = b.Email
where a.Id > b.Id

Data in the table after deleting duplicate data ：

Id	Email
1	[email protected]
2	[email protected]