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RE: SQL help with EXISTS



fixed

I don't think that is correct. It seems to do the subselect (return a set of rows) and THEN join the result to the outer select. A few responses have stated what you said - that EXISTS simply returns TRUE or FALSE. But I think that it must do this for each row in the outer select in the case where a join is occurring?

Maybe Im wrong, I don't know SQL and it is elusive and powerful and complex so I don't understand all the subtleties.



-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Dan Kimmel
Sent: Thursday, December 06, 2012 11:01 AM
To: Midrange Systems Technical Discussion
Subject: RE: SQL help with EXISTS

The EXISTS says "are there any". You get the same results in the outer select whether there's one or many results from the subselect.

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Stone, Joel
Sent: Thursday, December 06, 2012 10:54 AM
To: 'Midrange Systems Technical Discussion'
Subject: RE: SQL help with EXISTS

Thanks - you are correct - nothing to relate the outer query to the subselect. I must have deleted it :(

Please look at my recent post - if I drop the GROUP BY, result will have too many records I think - I only want ONE rec from outer select for each occurrence in file.


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Dan Kimmel
Sent: Thursday, December 06, 2012 10:50 AM
To: Midrange Systems Technical Discussion
Subject: RE: SQL help with EXISTS

You have nothing to relate the outer query to the subselect. Looks like you deleted the A. in front of ASHPNBR in the where clause. I think it should be:

select * from miscchg A
where
exists
(select ASHPNBR, ABLDNGD, AMSCHRG from MISCCHG where A.ASHPNBR = 'BN123456'
group by ASHPNBR,ABLDNGD, AMSCHRG )

By the way there's no need for all the fields in the subselect. You'd get the same results quicker with:

select * from miscchg A
where
exists
(select 1 from MISCCHG where A.ASHPNBR = 'BN123456'
group by ASHPNBR,ABLDNGD, AMSCHRG )

I don't think the group by is buying you anything, either.


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Stone, Joel
Sent: Thursday, December 06, 2012 10:23 AM
To: 'Midrange Systems Technical Discussion'
Subject: SQL help with EXISTS

I am pretty sure that the following selected only a few records from a large file (ASHPNBR = 'BN123456' ).

Then I changed a paren or something small and I cant get it to select only a few records - now it selects ALL values of ASHPNBR.

The sub-select works great and only selects a few records.

When I add the outer select, the entire file is selected (all ASHPNBR values).

How does EXISTS know which keys to join between the inner & outer query? Do I have to explicitly state the join? Or does "EXISTS" make assumption about which fields to join?

Thanks







select * from miscchg A
where
exists
(select ASHPNBR, ABLDNGD, AMSCHRG from MISCCHG where ASHPNBR = 'BN123456'
group by ASHPNBR,ABLDNGD, AMSCHRG )

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