Question

I have a table in this form:

id | firstname | lastname
---+-----------+----------
1  | alex      | marti
2  | mark      | finger
3  | alex      | marti
4  | ted       | port

Need to return the firstname, lastname duplicates in this form:

1  | alex      | marti
3  | alex      | marti

I tried doing select firstname, lastname from t group by firstname, lastname having count(*) > 1 but that will return something like

firstname | lastname
----------+----------
mark      | finger
alex      | marti
ted       | port

And I need the id of the duplicates but of course select id, firstname, lastname from t group by id, firstname, lastname won’t work.

Any ideas? Thanks.

Answer 1

You need to aggregate the id. If you need only the ID of one of them, for, say, deletion, you could do:

select max(id) id, firstname, lastname from t group by firstname, lastname having count(*) > 1

If you want both id’s and know there will never be more than 2, you could do the following:

select min(id) minid, max(id) maxid, firstname, lastname from t group by firstname, lastname having count(*) > 1

If you want all duplicates, along with their id’s, you’ll have to use a derived table, as in Nitin Midha’s answer.