Helen Borrie wrote:

>
> At 08:02 AM 21/04/2003 +0930, you wrote:
> >When a certain table is updated, it triggers a cascade of updates in
> >other tables, many of whose fields might not satisfy their CHECK
> >constraints.
> >
> >How is one to distinguish between these so that the user can be
> >presented with meaningful information?
> >
> >E.g. Field "Amount Remaining" in Table "Feed Inventory" has become
> >negative.
>
> You can create exceptions and use these in your triggers to return a
> "meaningful" message to the client. For example,
>
> create exception balance_negative ' "Amount Remaining" in Table "Feed
> Inventory" has become
> negative.'
>
> (I haven't done a character count on this but the message string does have
> a pretty short limit, I think about 70 characters...an incentive for
> writing tight messages :-) ))
>

Table T3:
F3a INTEGER CHECK(F2 >= 0)
F3b INTEGER CHECK(F3 >= 0)

Table T2: AU:
Update T3.F3a = -F2 // fails CHECK constraint here as -F2 = -56
Update T3.F3b = -F2

Table T1: AU:
Update T4.F4 = 60 // some other table that doesn't cause exception
Update T2.F2 = 56
Update T5.F5 = 68 // some other table that doesn't cause exception

When T1 is updated, INTEG_63 is violated: F3a >= 0.

Where in this do I specify the exception, as I dont' know what the
reason for the exception is in the AU of table T1?
--
Raymond Kennington
Programming Solutions
TeamW2W (InfoPower)