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Re: BUG #2178: NOT IN command don't work

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 (view raw or flat)
Thread:
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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