Re: Alternative to Select in table check constraint

This is more of an implementation option, but when I worry about what is
active/inactive I put start/end dates on the tables. Then you don't need
active indicators. You just look for the record where now() is >= start
date and now() <= end date or end date is null. You can even
activate/deactivate a badge on a future date. Of course, this complicates
the data integrity - you will need some kind of specialized trigger that
checks the data and makes sure there are no date overlaps to ensure you
don't have two badges active at the same time. But is also gives you a
history of badges and their activities.

-Aaron

On 6/30/06, Richard Broersma Jr <rabroersma(at)yahoo(dot)com> wrote:
>
> > > CHECK ( 1 = ALL ( SELECT COUNT(STATUS)
> > > FROM BADGES
> > > WHERE STATUS = 'A'
> > > GROUP BY EMPNO))
> >
> > From the PostgreSQL docs (http://www.postgresql.org/docs/8.1/
> > interactive/sql-createtable.html)
> >
> > CREATE UNIQUE INDEX one_a_badge_per_employee_idx
> > ON badges (empno)
> > WHERE status = 'A';
> > http://www.postgresql.org/docs/8.1/interactive/sql-createindex.html
> > http://www.postgresql.org/docs/8.1/interactive/indexes-partial.html
>
> Michael,
>
> Partial indexs seem to be "what the doctor ordered!" And your suggest is
> right on, the idea of
> the constraint is to allow only one active badge status at a time.
>
> But now that I think about it, using the authors suggestion (if it
> actually worked), how would
> would it be possible to change the active status from one badge to
> another?
>
> Oh well, partial index are obvious the superior solution since the entire
> table doesn't not have
> to be scanned to determine if the new badge can be set to active.
>
> Once again thanks for the insight.
>
> Regards,
>
> Richard Broersma Jr.
>
>