leetcode_gym/_problems/sql_delete_duplicate_emails.md

layout, title, last_solved, category, leetcode_url, status

layout	title	last_solved	category	leetcode_url	status
page	Delete Duplicate Emails		sql	https://leetcode.com/problems/delete-duplicate-emails	Attempted

Problem

Write a SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id.

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+
Id is the primary key column for this table.
For example, after running your query, the above Person table should have the following rows:

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+

Solution

For deletion, start with selection, then modify to deletion

{% highlight sql %}

select a.* from person a join person b on a.email=b.email where a.id > b.id

{% endhighlight %}

{% highlight sql %}

delete a from person a join person b on a.email=b.email where a.id > b.id

{% endhighlight %}