从子查询结果中删除ID

Question

Lets say I have this users table:

id email
1  test@gmail.com
2  xxp@gmail.com
3  test@gmail.com
4  zzz@gmail.com

And I want to delete rows that have duplicated emails .

First I thought of retrieving duplicated emails:

select id
group by email
having count(*)>1

Which results in:

updated result

1

Then I added the delete clause:

delete from users
where id in(
    select id
    group by email
    having count(*)>1 )

The result is No Errors, but 0 rows affected... which means nothing happened.

I want to know what I'm doing wrong and some other ways of doing this.

Specifications: MySQL 5.5.5-10.1.16-MariaDB Using Sequel Pro on Mac

Thanks

Answer 1

You can do a sub-query to get the id or ids having duplicate then remove it from your table. See demo here: http://sqlfiddle.com/#!9/f14d05/1

DELETE from users 
where id in (
     SELECT id 
     from (
           SELECT a.id, count(*) as rn 
             FROM users a
            JOIN users b ON a.email = b.email AND a.id <= b.id
           GROUP BY a.id, a.email
          )  t
      where rn>1
      );

Answer 2

Tested on MSSQL.

select min(id) id, email 
into #users 
from [users]
group by email

delete from [users] where id not in (select id from #users)

drop table #users