Finding period NOT in a table

Is there an easy way to find which of a set of numbers isn't in a table? I'm trying to find financial periods that are missing from a set of data. I can do it if I have a table which just contains the valid period numbers 1- 12 in the following way:

SELECT
     period_num
FROM
     valid_periods
WHERE
      period_num NOT IN (SELECT DISTINCT data_period FROM data_table)

But is there a simple way to do it without the valid_periods table? Received on Tue Aug 21 2007 - 09:14:22 CDT