How to delete duplicate rows without unique identifier

Question

I have duplicate rows in my table and I want to delete duplicates in the most efficient way since the table is big. After some research, I have come up with this query:

WITH TempEmp AS
(
SELECT name, ROW_NUMBER() OVER(PARTITION by name, address, zipcode ORDER BY name) AS duplicateRecCount
FROM mytable
)
-- Now Delete Duplicate Records
DELETE FROM TempEmp
WHERE duplicateRecCount > 1;

But it only works in SQL, not in Netezza. It would seem that it does not like the DELETE after the WITH clause?

Answer 1

If you have no other unique identifier, you can use ctid:

delete from mytable
    where exists (select 1
                  from mytable t2
                  where t2.name = mytable.name and
                        t2.address = mytable.address and
                        t2.zip = mytable.zip and
                        t2.ctid > mytable.ctid
                 );

It is a good idea to have a unique, auto-incrementing id in every table. Doing a delete like this is one important reason why.