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From: "Arjan van Bentem" <avbentem@DONT-YOU-DAREdds.nl>
Newsgroups: comp.databases.oracle.server
Subject: Re: Char vs Varchar2 and NULL
Date: Wed, 9 Sep 1998 19:17:43 +0200
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>I am told but have not checked, that
>IF NULL = NULL THEN
>will always evaluate to false

Indeed. When in doubt think of it as 'undefined' or 'X'. Here, the value of
unkown X would set the result:

    ( null and true ) = ( X and true ) = X = null
    ( null or false ) = ( X or false ) = X = null

But in the next two examples, it would not matter what value X has:

    ( null or true ) = ( X or true ) = true
    ( null and false ) = ( X and false ) = false

Well, when evaluating ( null = null ), you'd need to think of ( X = Y ).

Arjan.