From: | "Jean-Pierre Pelletier" <pelletier_32(at)sympatico(dot)ca> |
---|---|
To: | "Daniel Afonso Heisler" <daniel(at)solis(dot)coop(dot)br> |
Cc: | <pgsql-bugs(at)postgresql(dot)org> |
Subject: | Re: BUG #2178: NOT IN command don't work |
Date: | 2006-01-24 16:56:45 |
Message-ID: | BAYC1-PASMTP0442C4EBB587635B8521F195130@CEZ.ICE |
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Lists: | pgsql-bugs |
The expected behavior can be obtained by filtering out the null in
the subquery or by using "not exists" instead of "not in".
Here is an example:
CREATE TEMPORARY TABLE subquerytable (column1 INTEGER);
INSERT INTO subquerytable VALUES(2);
INSERT INTO subquerytable VALUES(NULL);
INSERT INTO subquerytable VALUES(3);
SELECT true WHERE 1 NOT IN (SELECT column1 FROM subquerytable); -- Wrong
SELECT true WHERE 1 NOT IN (SELECT column1 FROM subquerytable WHERE column1
IS NOT NULL); -- Ok
SELECT true WHERE NOT EXISTS(SELECT * FROM subquerytable WHERE 1 =
column1); -- Ok
It's not clear to me why "not exists" and "not in" return a different result
but it must be per SQL spec
as all DBMS I have seen do that (Oracle, SQL Server, MYSQL, ...)
In most queries I have seen column1 is NOT NULL so IN or EXISTS can both be
used safely.
Jean-Pierre Pelletier
e-djuster
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