Re: Jan's well-defined view updates definition

mikharakiri_at_yahoo.com (Mikito Harakiri) wrote in message news:<bdf69bdf.0309151944.606515f3_at_posting.google.com>...
> > > For example, suppose we have
> > >
> > > Q1 = (SELECT name
> > > FROM Emps
> > > WHERE dept = "sales"
> > > )
> > > Q2 = (SELECT name
> > > FROM Emps
> > > WHERE dept <> "sales"
> > > )

Better example would be

Q1 = (SELECT name
  FROM Emps as D
  WHERE dept = "sales"
)
Q2 = (SELECT name, dept
  FROM Emps as D
  WHERE dept <> "sales"
)

Perfectly updateable view, no constraint is necessary. The inverse view is

Q^(-1) = (
  select name, 'sales' as dept from EmpsTr as V1   union
  select name, dept from V2
) Received on Tue Sep 16 2003 - 18:56:50 CEST