Separate PK in Jxn Tbl?
On Feb 1, 12:30 am, "Brian Selzer" wrote:
"Roy Hann" wrote in message
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.
Yes. In addition, if the client code knows what the database's
constraints
are, it can provide better user experience, better error messages,
etc.
Marshall
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