Re: Separate PK in Jxn Tbl?

From: Brian Selzer <>
Date: Fri, 01 Feb 2008 08:30:12 GMT
Message-ID: <oMAoj.5076$>

"Roy Hann" <specially_at_processed.almost.meat> wrote in message
> "Brian Selzer" <> wrote in message
> news:p9uoj.5279$
>> Constraints should always be checked by the DBMS, not by applications.
> I agree very heartily with the first part of this statement, for the
> reasons you give below. I disagree with the second part (as stated).
> There is no reason why applications shouldn't also test what constraints
> they can. The problem is that they should not have hand-coded
> re-implementations of the constraints because those will get out of sync
> with the database over time. What would be very nice is if one day it were
> possible for applications to download the relevant constraints at
> run-time, the way they presently download other metda-data.

That's a good point. I should have said instead, "Constraints should always be /enforced/ by the DBMS, not by applications." It is often a good thing for an application to do some checking because it can reduce the number of round-trips, and maybe even some transaction rollbacks.

>> If you have two separate applications that manipulate the same table, and
>> one enforces one constraint while another enforces another, then all you
>> need to do to bypass one constraint is to use the other application!
>> What, then, is the point of even having the constraint?
> Roy
Received on Fri Feb 01 2008 - 09:30:12 CET

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