OK, I guess I stepped on a nerve here...and in retrospect, I should
have thought out my post more....
-I should not have made a reference to SQL Server...the IS NULL
operator is part of the ANSI-92 standard, and would be used in any
database that conforms to that(but the original post was referring to
SQL Server :-)) . But the question was why "IS NULL"...it is a syntax
thing...the "IS" operator is used for nothing else that I know of. It
allows the database engine to override the rule that NULL = NULL
resolves to "Unknown" and actually do the comparison, treating NULL as
a "value" ("value" is in quotes so no one jumps down my throat,
going..."NULL has no value!!!"...that is understood).
-The assignment issue is not completely obvious to me....and this is
more of an overall issue with the ANSI-92 standard than with
assignment vs comparison...in some ways, I think having a special
syntax for the assignment of NULL would have helped people understand
the concept. I also don't think database systems should default
fields to allow NULL if it is not specified(as SQL Server does).
-This is part of the SQL Standard, and IS probably the best way to
handle NULLs, but there are exceptions...that is why you have
conditions like SET ANSI_NULLS OFF. The fact is that the concept of
three value logic is not that straight forward to everyone, and
including it in the SQL spec has probably confused a lot of people.
--
Jim Wright
Wright Business Solutions
[EMAIL PROTECTED]
919-417-2257
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