| From: | Rene Pijlman <reageer(dot)in(dot)de(dot)nieuwsgroep(at)onzin-adres(dot)nl> |
|---|---|
| To: | pgsql-general(at)postgresql(dot)org |
| Subject: | Re: very big problem with NULL |
| Date: | 2001-06-08 17:34:34 |
| Message-ID: | g132it43h7uc3se0hhcmed89993kbdk76a@4ax.com |
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| Lists: | pgsql-general |
Grant <grant(at)xactcommerce(dot)com> schreef:
>However, the last time i checked, NULL does not equal to 1, 2, 3, or
>anything else besides NULL. Thats why I'm confused as to why SELECT column
>FROM table WHERE column != 1 also excludes NULL, because 1 does NOT have the
>same value as NULL.
NULL is unknown. Therefore, it is unknown if NULL equals 1, and it is
also unknown if NULL does not equal 1.
NULL = 1 --> NULL
NULL != 1 --> NULL
That's why SQL has the special operator IS NULL and IS NOT NULL (or
NOT IS NULL, I allways forget which one).
--
Vriendelijke groet,
René Pijlman <rpijlman(at)spamcop(dot)net>
Wat wil jij leren?
http://www.leren.nl/
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