--!sql
 
-- table people
 
 id | name 
----+------
  1 | jan
  2 | jan
  3 | pol
  4 | jan
  5 | pol
  6 | anna
 
 
-- select all oldest records that have duplicates (oldest = with lower id)
SELECT id FROM people WHERE EXISTS(
   SELECT * FROM people AS tmp WHERE tmp.id > people.id AND tmp.name = people.name
);
 
 
 id
----
  1
  2
  3
 
 
-- delete duplicates
DELETE FROM PEOPLE WHERE id IN (
   SELECT id FROM people WHERE EXISTS(
      SELECT * FROM people AS tmp WHERE tmp.id > people.id AND tmp.name = people.name
   )
);