For example: SELECT nullablecol FROM tab WHERE nullablecol = <value>;
If the equality operator is strict then the nullablecol can be NULL in the WHERE clause but not in the SELECT list. Tom's idea should allow us to determine both of those things but your idea cannot tell them apart, so, in theory at least, Tom's idea seems better to me.
David
That's really something I can't do, thanks for the explanation.
