Re: "= null" & "is null"

From: Ed Prochak <prochak_at_my-deja.com>
Date: Thu, 26 Aug 1999 13:01:56 GMT
Message-ID: <7q3drr$lis$1@nnrp1.deja.com>

In article <7q3936$37f$2_at_imsp009a.netvigator.com>, Norris <johnnie_at_cooper.com.hk> wrote:
> What is the difference between = null and is null?
>
> --
> --
> http://www.washington.edu/pine/faq/
>

Time for you to review SQL's three valued logic. To relate this to your question, consider these examples:

where X is NULL
This condition is always either TRUE or FALSE.

where X = NULL
This condition is always FALSE.

Consider that second example for a moment. NULL means no value set, ie the value is UNKNOWN. SOoo..

...if X has a value then X=NULL is obviously FALSE.

...if X is NULL then its value is UNKNOWN and X=NULL cannot be determined. So it gets treated as if it is FALSE.

--
Ed Prochak
Magic Interface, Ltd.
ORACLE services
440-498-3700 <<<NOTE new number

Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't. Received on Thu Aug 26 1999 - 08:01:56 CDT