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Re: Subquery with null returns

From: Tanel Poder <tanel_at_@peldik.com>
Date: Fri, 28 Mar 2003 12:29:57 +0200
Message-ID: <3e842366$1_2@news.estpak.ee> 





> Because NULL values are discarded in joins, subqueries, correlated

> subqueries and comparison operators, "=","!=", ">" etc. That is the

> correct behaviour, because NULL is not comparable to anything, not

> even another NULL :




Hi!



In addition to Kenneths post, NULL means "unknown" in relation database
theory. Naturally, you can't compare anything with unknown value.



Tanel.
Received on Fri Mar 28 2003 - 04:29:57 CST












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