Using a variable period in an interval in Postgres

Question

I have a relation that maintains monthly historical data. This data is added to the table on the last day of each month. A service I am writing can then be called specifying

Answer 1

This code has nothing directly to do with your situation, but it does illustrate how to use variables in INTERVAL arithmetic. My table's name is "calendar".

CREATE OR REPLACE FUNCTION test_param(num_months integer)
  RETURNS SETOF calendar AS
$BODY$

    select * from calendar
    where cal_date <= '2008-12-31 00:00:00'
    and cal_date > date '2008-12-31' - ($1 || ' month')::interval;

$BODY$
  LANGUAGE sql VOLATILE
  COST 100
  ROWS 1000;