PostgreSQL Removing duplicates

Question

I am working on postgres query to remove duplicates from a table. The following table is dynamically generated and I want to write a select query which will remove the recor

Answer 1

             select count(first) as cnt, first, second 
             from df1 
             group by first
             having(count(first) = 1)

if you want to keep one of the rows (sorry, I initially missed it if you wanted that):

             select first, min(second) 
             from df1 
             group by first

Where the table's name is df1 and the columns are named first and second.

You can actually leave off the count(first) as cnt if you want.

At the risk of stating the obvious, once you know how to select the data you want (or don't want) the delete the records any of a dozen ways is simple.

If you want to replace the table or make a new table you can just use create table as for the deletion:

             create table tmp as 
             select count(first) as cnt, first, second 
             from df1 
             group by first
             having(count(first) = 1);

             drop table df1;

             create table df1 as select * from tmp;

or using DELETE FROM:

DELETE FROM df1 WHERE first NOT IN (SELECT first FROM tmp);

You could also use select into, etc, etc.