Date: Sun, 17 Feb 2013 22:26:35 +0000
From: Ben Morrow <ben@morrow.me.uk>
To: maps.on@gmx.net, pgsql-sql@postgresql.org
Subject: Re: How to reject overlapping timespans?
Message-ID: <20130217222632.GA36320@anubis.morrow.me.uk>
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Quoth maps.on@gmx.net (Andreas):
> Am 17.02.2013 19:20, schrieb Andreas Kretschmer:
> > Andreas <maps.on@gmx.net> hat am 17. Februar 2013 um 18:02 geschrieben:
> >> I need to store data that has a valid timespan with start and enddate.
> >>
> >> objects ( id, name, ... )
> >> object_data ( object_id referencs objects(id), startdate, enddate, ... )
> >>
> >> nothing special, yet
> >>
> >> How can I have PG reject a data record where the new start- or enddate
> >> lies between the start- or enddate of another record regarding the same
> >> object_id?
> >
> > With 9.2 you can use DATERANGE and exclusion constraints
> 
> though I still have a 9.1.x as productive server so I'm afraid I have to 
> find another way.

If you don't fancy implementing or backporting a GiST operator class for
date ranges using OVERLAPS, you can fake one with the geometric types.
You will need contrib/btree_gist to get GiST indexes on integers.

    create extension btree_gist;

    create function point(date) 
    returns point
    immutable language sql
    as $$ 
        select point(0, ($1 - date '2000-01-01')::double precision)
    $$;

    create function box(date, date)
    returns box
    immutable language sql
    as $$ 
        select box(point($1), point($2))
    $$;

    create table objects_data (
        object_id   integer     references objects,
        startdate   date,
        enddate     date,
        exclude using gist
            (object_id with =, box(startdate, enddate) with &&)
    );

You have to use 'box' rather than 'lseg' because there are no indexes
for lsegs. I don't know how efficient this will be, and of course the
unique index will probably not be any use for anything else.

Ben


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