Claudio,

there is one thing that I think you do not understand. NULL is not a value,
it is a state. That is one reason for it not being possible to write
something like

SELECT <something>
FROM <somewhere>
WHERE <field> = NULL

NULL simply means unknown. E.g. I expect you are not that much of a soccer
fanatic that you know the Norwegian league very well. But the fact that you
do not know how many points Bryne and Viking have doesn't mean that they
have the same number of points. You simply don't know (and I won't tell you
;o). To separate the state of unknown from known values it is treated
differently, e.g. by having to specify IS NULL rather than = NULL in where
clauses.

Set