SET,

S> So to me it isn't that obvious that NULL IS NULL should
S> return true...

regardless of how much it is obvious or not, the expression (NULL IS
NULL) does return true. That's exactly why the IS NULL operator
exists. The problem with Firebird is that it insists on wanting to
know the data type of every expression operand. It has always been
this way in IB AFAIR. In DSQL, if you supply a value for a parameter
then the data type in inferred from the value; if you supply null,
you're stuffed.
Note that there's no such problem in PSQL, as parameters and variables
there are explicitly declared and as such all have a data type.
Firebird should probably find a way to do without a data type in
expressions involving all nulls, like other RDBMSs do.

Ciao
--
Nando Dessena
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