There are a number of different ways to achieve this, depending on what you are trying to achieve. Usually, you are trying to remove duplication of a certain key due to changes in business rules or recognition of a business rule that was not applied when the database was originally built.

Probably the quickest method is to build a copy of the original table:

select *

into temp_table

from base_table

where 1=0

Create a unique index on the columns that covers the duplicating rows with the ignore_dup_key attribute. This may be more columns that the key for the table.

create unique index temp_idx

on temp_table(col1, col2, ..., colN)

with ignore_dup_key

Now, insert base_table into temp_table.

insert temp_table

select * from base_table