From: | Rene Pijlman <reageer(dot)in(at)de(dot)nieuwsgroep> |
---|---|
To: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: not null - trivial, unexpected behavior |
Date: | 2001-06-16 15:28:06 |
Message-ID: | odumit8vqilkh2l9kfiljlj88oa0e4e2fk@4ax.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-sql |
jmscott(at)yahoo(dot)com (John Scott) schreef:
>select count(*) from A where b = null; /* Returns 1, ok */
>select count(*) from A where b != null; /* Returns 0 ... not ok! */
>
>What am i missing?
The documentation :-)
"To check whether a value is or is not NULL, use the constructs
expression IS NULL
expression IS NOT NULL
Do not use expression = NULL because NULL is not "equal to" NULL.
(NULL represents an unknown value, so it is not known whether two
unknown values are equal.) Postgres presently converts x = NULL
clauses to x IS NULL to allow some broken client applications (such as
Microsoft Access) to work, but this may be discontinued in a future
release."
http://www.postgresql.org/users-lounge/docs/7.1/postgres/functions-comparison.html
Regards,
René Pijlman
http://www.applinet.nl
From | Date | Subject | |
---|---|---|---|
Next Message | Peter Eisentraut | 2001-06-16 16:11:54 | Re: not null - trivial, unexpected behavior |
Previous Message | John Scott | 2001-06-16 15:16:11 | not null - trivial, unexpected behavior |