title: SQL: Get list of numbers not in use by other rows
body: <p>I'm using PostgreSQL 8.1.17, and I have a table with account numbers. The acceptable range for an account number is a number between 1 and 1,000,000 (a six digit number). The column "acctnum" contains the account number. Selecting all the numbers in use is easy (SELECT acctnum FROM tbl_acct_numbers ORDER BY acctnum). What I would like to do is select all the numbers in the acceptable range that are not in use, that is, they aren't found in any rows within the column acctnum.</p>