Efficiently delete duplicates rows from a table with a set of specific constraints.

delete_duplicates.sql

DELETE FROM <table> a USING (
SELECT MIN(ctid) as ctid, var1, var2
  FROM <same_table> b
  GROUP BY 2,3 HAVING COUNT(*) > 1
) b
WHERE a.var1 = b.var1
and a.var2 = b.var2
AND a.ctid <> b.ctid