Sorry to bug you with what is a simple question but if you could point me in
the right direction I can follow up.
I have a sql table field we can call XXX it is the least significant of a
four field primary key (aaa bbb ccc).
When XXX is of the form A99 (i.e. the letter A followed by two digits) I
want to ensure that it is the only aaa bbb ccc of that form.
If I had a function ISof FormA99(XXX) that returned either "T" when it was
or "F" || XXX my key constraint would be that aaa bbb ccc ISof FormA99(XXX)
is unique.
My question is: how do I do this? If there was such a thing (is there?) as
a derived field then I would create the function and use a unique
constraint. I am sure there are many ways to do this. This table will be
small (1000 rows at most) and change infrequently.
Thanks