Delete duplicate rows (don't delete all duplicate)

Question

I am using postgres. I want to delete Duplicate rows. The condition is that , 1 copy from the set of duplicate rows would not be deleted.

i.e : if there are 5 duplicate records then 4 of them will be deleted.

Answer 1

Try the steps described in this article: Removing duplicates from a PostgreSQL database.

It describes a situation when you have to deal with huge amount of data which isn't possible to group by.

A simple solution would be this:

DELETE FROM foo
       WHERE id NOT IN (SELECT min(id) --or max(id)
                        FROM foo
                        GROUP BY hash)

Where hash is something that gets duplicated.