I have never seen a file that is not "uniquely keyed".
Have you ever used transaction files with of multiple (a few hundreds)
columns?
Even if you think you found an unique key it may not be unique!
Mit freundlichen Grüßen / Best regards
Birgitta Hauser
"Shoot for the moon, even if you miss, you'll land among the stars." (Les
Brown)
"If you think education is expensive, try ignorance." (Derek Bok)
"What is worse than training your staff and losing them? Not training them
and keeping them!"
-----Ursprüngliche Nachricht-----
Von: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] Im Auftrag von Matt Olson
Gesendet: Friday, 28.12 2012 20:26
An: 'Midrange Systems Technical Discussion'
Betreff: RE: Uniquely identifying a record in SQL without a unique key?
I have never seen a file that is not "uniquely keyed". There is always some
combination of fields (composite key) that makes up a way of uniquely
identifying a record.
The only time this would matter is if you had a two identical records in a
table.
But then this begs two questions:
1. Why is there duplicate data with no difference in any of the columns.
2. Why is there not a unique key column, or composite key on the table.
In either of the two cases above the developer did something very bad.
-----Original Message-----
From: James H. H. Lampert [mailto:jamesl@xxxxxxxxxxxxxxxxx]
Sent: Friday, December 28, 2012 12:54 PM
To: 'Midrange Systems Technical Discussion'
Subject: Uniquely identifying a record in SQL without a unique key?
I'm beginning to study Scott Klement's JDBCR4 API, as a means of extending
our QuestView product to access external databases (and it would also allow
us to expand our very limited support of data types that are normally
SQL-only), and something suddenly struck me:
Suppose I'm looking at a record, and I decide to make a change to it.
And the file isn't uniquely keyed.
Now, with native RLA, we can easily determine the RRN of the record we're
looking at, and acquire an update lock on that record by its RRN.
After all, RRNs only change if a RGZPFM is done, and that requires an
exclusive lock on the member.
But now, suppose I have to use SQL, JDBC, and the JDBCR4 API. I'm no expert
on SQL (SQL for Dummies is still my primary reference on the subject), but I
don't recall ever reading anything anywhere about a way to get a record's
RRN, or retrieve a record by its RRN, from SQL.
I must be missing *something* here, but what? How do I guarantee that an
update will go to the right record, when I initially read it without a lock,
and apparently can't grab a lock on it by its RRN?
--
JHHL
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