The following bug has been logged online:
Bug reference: 4057
Logged by: Reginald Drake
Email address: reggie(dot)drake(at)gmail(dot)com
PostgreSQL version: 8.2.7
Operating system: Ubuntu linux
Description: SUM returns NULL when given no rows
Details:
Doing something like "SELECT SUM(some_integer_column) FROM some_table WHERE
FALSE" gives me NULL, where I would expect 0. Since COUNT does give a
meaningful value when applied to zero columns, maybe SUM should do the same.