Re: exists <==> not exists ???

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