RE: Classic trap : using SQL while not fully competent

David,

In your original query, the WHERE clause looks at the entire joined record; after the join has been
accomplished.

However, you said yourself that the tcrtcd field was from the right hand file and there wasn't a
record in the right. Thus no wonder the DB couldn't find a record that met the where clause.

In other words, consider the results set from the following:
SELECT * FROM prdcap exception join adhtst on ad1cad=tadhno

The only records that will be returned have NULL for all fields on the right. That's what an
exception join does. Thus when you add a WHERE tcrtcd ='14', it is impossible for any rows to match.

HTH,

Charles Wilt
Software Engineer
CINTAS Corporation - IT 92B
513.701.1307

wiltc@xxxxxxxxxx

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-
bounces@xxxxxxxxxxxx] On Behalf Of David FOXWELL
Sent: Thursday, April 03, 2008 5:46 AM
To: Midrange Systems Technical Discussion
Subject: Classic trap : using SQL while not fully competent

I was going to cry for help :

I know I have a record on the left that ain't on the right so I did

SELECT * FROM prdcap exception join adhtst on ad1cad=tadhno
WHERE tcrtcd ='14'

Which returned no record.


But

SELECT * FROM prdcap WHERE P ad1cad not in
( select tadhno from adhtst where tcrtcd ='14')

Found the record.

After a while I thought, maybe its because tcrtcd is in the right hand
table, so I tried
SELECT * FROM prdcap exception join adhtst on ad1cad=tadhno
and tcrtcd = '14'

Which worked.

Its the first time I put the where criteria in the JOIN. Can anyone give
me the technical explication as to why the first example didn't work so I
don't fall in again please ?

Thanks.

--
This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing
list
To post a message email: MIDRANGE-L@xxxxxxxxxxxx
To subscribe, unsubscribe, or change list options,
visit: http://lists.midrange.com/mailman/listinfo/midrange-l
or email: MIDRANGE-L-request@xxxxxxxxxxxx
Before posting, please take a moment to review the archives
at http://archive.midrange.com/midrange-l.

This e-mail transmission contains information that is intended to be confidential and privileged. If you receive this e-mail and you are not a named addressee you are hereby notified that you are not authorized to read, print, retain, copy or disseminate this communication without the consent of the sender and that doing so is prohibited and may be unlawful. Please reply to the message immediately by informing the sender that the message was misdirected. After replying, please delete and otherwise erase it and any attachments from your computer system. Your assistance in correcting this error is appreciated.