Обсуждение:

On Thu, 2005-10-13 at 10:31, Shavonne Marietta Wijesinghe wrote:
> how can i do a query with 2 databases??

This is only supported by an add on called dblink, and it's a little bit
klunky.

Could schemas solve your problem?

Hi,

I have just run this command on 8.0.4 :

SELECT 'foo' WHERE 0 NOT IN (NULL, 1);

And it resulted is zero rows.
Without NULL it is OK.
Is this a bug, or the standard has such a rule?

Best Regards,
Otto

Havasvölgyi Ottó wrote:
> Hi,
> 
> I have just run this command on 8.0.4 :
> 
> SELECT 'foo' WHERE 0 NOT IN (NULL, 1);

0 <> NULL   (Indeed nothing equals NULL, other then sometimes NULL itself)

0 <> 1

Therefore, the statement: 0 NOT IN (NULL, 1)
Should always equate to false.

Therefore No rows returned.  Ever.

Terry
> 
> And it resulted is zero rows.
> Without NULL it is OK.
> Is this a bug, or the standard has such a rule?
> 
> Best Regards,
> Otto
> 
> 
> 
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-- 
Terry Fielder
terry@greatgulfhomes.com
Associate Director Software Development and Deployment
Great Gulf Homes / Ashton Woods Homes
Fax: (416) 441-9085

As i understand it, the use of NULL in SQL means the value of the column
is unknown.  Therefore that result would seem fair.

Havasvölgyi Ottó wrote:
> Hi,
>
> I have just run this command on 8.0.4 :
>
> SELECT 'foo' WHERE 0 NOT IN (NULL, 1);
>
> And it resulted is zero rows.
> Without NULL it is OK.
> Is this a bug, or the standard has such a rule?
>
> Best Regards,
> Otto
>
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Have you searched our list archives?
>
>               http://archives.postgresql.org
>

Havasvölgyi Ottó <h.otto@freemail.hu> writes:
> I have just run this command on 8.0.4 :

> SELECT 'foo' WHERE 0 NOT IN (NULL, 1);

> And it resulted is zero rows.
> Without NULL it is OK.
> Is this a bug, or the standard has such a rule?

This is per spec.

The computation is effectivelyNOT (0 = NULL OR 0 = 1)NOT (NULL OR FALSE)NOT NULLNULL
ie, the result is UNKNOWN, which WHERE treats the same as FALSE.
        regards, tom lane

On Wed, 19 Oct 2005, [iso-8859-2] Havasv�lgyi Ott� wrote:

> Hi,
>
> I have just run this command on 8.0.4 :
>
> SELECT 'foo' WHERE 0 NOT IN (NULL, 1);
>
> And it resulted is zero rows.
> Without NULL it is OK.
> Is this a bug, or the standard has such a rule?

This is standard behavior.

Seeing if I can do this from memory...

a NOT IN b is equivalent in the spec to NOT(a IN b). a IN b is equivalent
to a =ANY b. a =ANY b returns true if a = x is true for any x in b. a =ANY
b returns false if a = x is false for all x in b.  Otherwise it returns
unknown.

0 = NULL returns unknown
0 = 1 returns false
So, 0 IN (NULL,1) returns unknown.

NOT(unknown) is unknown.

WHERE clauses only return rows for which the search condition is true, so
a row is not returned.