exists <==> not exists ???

Christian Breimann <chr@math.uni-muenster.de> writes:

When executing a SQL-Query with a "where not exists (...)" Statement,
the result is wrong. It's the same result as I execute "where exists
(...)" This mustn't be true.

This is a completely unhelpful bug report. We need sufficient details
to let us reproduce the problem.

regards, tom lane

How do I stop this information from coming to me?

-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Sent: Friday, May 11, 2001 9:35 AM
To: Christian Breimann
Cc: pgsql-bugs@postgresql.org
Subject: Re: [BUGS] exists <==> not exists ???

Christian Breimann <chr@math.uni-muenster.de> writes:

When executing a SQL-Query with a "where not exists (...)" Statement,
the result is wrong. It's the same result as I execute "where exists
(...)" This mustn't be true.

This is a completely unhelpful bug report. We need sufficient details
to let us reproduce the problem.

regards, tom lane

---------------------------(end of broadcast)---------------------------
TIP 4: Don't 'kill -9' the postmaster

Christian Breimann <chr@math.uni-muenster.de> writes:

select distinct S.customer_name
from depositor as S
where not exists(
(select branch_name
from branch
where branch_city='Brooklyn')
except
(select R.branch_name
from depositor as T, account as R
where T.account_number = R.account_number
and S.customer_name = T.customer_name)
);

Ah. In current sources I get correct (I think) results:

customer_name
----------------------
Johnson
(1 row)

customer_name
----------------------
Hayes
Jones
Lindsay
Smith
Turner
(5 rows)

Your query is running into the same bug someone else discovered a few
days ago:

2001-05-08 15:47 tgl

* src/backend/executor/: nodeAppend.c, nodeSubqueryscan.c
(REL7_1_STABLE), nodeAppend.c, nodeSubqueryscan.c: Append and
SubqueryScan nodes were not passing changed-parameter signals down
to their children, leading to misbehavior if they had any children
that paid attention to chgParam (most plan node types don't).
Append's bug has been there a long time, but nobody had noticed
because it used to be difficult to create a query where an Append
would be used below the top level of a plan; so there were never
any parameters getting passed down. SubqueryScan is new in 7.1 ...
and I'd modeled its behavior on Append :-(

The fix will be in 7.1.2 (due out real soon now), or you can pull
current REL7_1_STABLE sources from our CVS server if you are in a hurry.

Thanks for the report!

regards, tom lane