Re: Possible problems with Date & McGoveran View Updating

"Jan Hidders" <jan.hidders_at_pandora.be> wrote in message news:PX38b.14807$2Z.580673_at_phobos.telenet-ops.be...
> A small example. Suppose we have a table Emps(name,dept) and a view TrEmps
> defined by
>
> SELECT name
> FROM Emps
> WHERE dept = "sales";
>
> then if you add a tuple to this view it is perfectly clear which tuple
> should be added to Emps and so this is a well-defined update.

This view is not updateable. If you delete a tuple from this view, do you delete from the base table or update dept = 'sales' into some other value (which we can't deduce from TrEmps alone)?

I was tempted to transform equation

(select name from Emps WHERE dept = 'sales') * Emps(name,dept) = TrEmps(name)

into

Emps(name,dept) = (select name, 'sales' from TrEmps) * TrEmps(name)

but this is obviously wrong. Received on Fri Sep 12 2003 - 16:02:37 CDT