Re: Finding overlapping records

I think you are right about the other cases. Especially about the case
where the newer lease resides entirely inside the older lease. I noticed
that one right after I sent the email last night and updated my trigger for
it.

As for the other ones, I was just depending on the order in the lease file
to protect me.

We're still on 8.2 for now. I started to look at the period data type from
John Davis and will play with it today.

On Thu, Dec 10, 2009 at 11:15:38AM -0600, Jon Erdman wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
>
> Doh. Just read your whole message, so I see why you were only checking
> for the one case. I think the full discussion is still worthwhile though.
>
> Jon Erdman wrote:
> >
> > Frank,
> >
> > First of all, you've got a big hole in your overlap check. You're only
> > checking for (new span is --- existing is +++):
> >
> > *+++++++*
> > *-------*
> >
> > when you really need to check for:
> >
> > *++++++++*
> > *---------*
> > *-------*
> > *--------------*
> > *---*
> >
> > /me pulls out Celko's SQL For Smarties...
> >
> > So what you would naturally write is perhaps (s1 and e1 are start and
> > end of existing span, s2 and e2 are the new span):
> >
> > WHERE
> > s2 between s1 and e1
> > OR e2 between s1 and e1
> > OR s1 between s2 and e2
> > OR e1 between s2 and e2;
> >
> > which is a bit long and ugly. There's a shortcut you can take, here's
> > how you would search for things that *don't* overlap:
> >
> > *+++++*
> > *----*
> > *-----*
> >
> > so you can write it as:
> >
> > WHERE NOT ((e2 < s1) OR (s2 > e1));
> >
> > which is *much* cleaner, no? ;)
> >
> > Credit goes to Joe Celko, SQL for Smarties, Chapter 13: Between and
> > Overlaps Predicate, 13.2 Overlaps Predicate, page 279.
> >
> > Postgres actually has OVERLAPS, so you can just say:
> >
> > WHERE (s2, e2) OVERLAPS (s1, e1);
> >
> > however, at least in 8.1, that doesn't use the indexes on the start_date
> > and end_date. The shortcut above does use those indexes and is nice and
> > fast.
> >
> > You should test and see if 8.3 or 8.4 will use the indexes for OVERLAPS
> > though...
>
> - --
>
> Jon T Erdman
>
> Chief Information Officer voice: (210) 400-5717
> Progressive Practice, Inc. jon(at)progressivepractice(dot)com
> P.O. Box 17288 www.progressivepractice.com
> Rochester, NY 14617
>
>
> -----BEGIN PGP SIGNATURE-----
>
> iEYEARECAAYFAkshLLoACgkQRAk1+p0GhSFVoQCePh1qJeljm6M294ItqKmO36a9
> mvoAn2qo1uzd0keVZe8XfH6Zg5DI6XS1
> =0/8a
> -----END PGP SIGNATURE-----