Edzard Pasma wrote:
There is a difference in the behaviour of GROUP BY in version 3.2.6. If you group by a column that contains NULL values, each NULL value comes on a seperate output line. Conceptually not so bad, if we read NULL as "unknown" and not as "empty". But I guess it is an error.
This does indeed appear to be an error: see http://archives.postgresql.org/pgsql-sql/1999-05/msg00164.php for a discussion which cites the SQL-92 specification as saying that two NULLs are considered "not distinct" and therefore should be grouped together.
MSSQL (and its parent Sybase) document that nulls will be grouped together.
