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Re: Heirarchical Data Structures. MS Access. Together?

From: Lennart Jonsson <lennart_at_kommunicera.umea.se>
Date: 28 Jul 2003 12:46:26 -0700
Message-ID: <6dae7e65.0307281146.114a865b@posting.google.com>


Heinz Huber <hhuber_at_racon-linz.at> wrote in message news:<3f252d63$0$48902$91cee783_at_newsreader02.highway.telekom.at>...
> Lennart Jonsson wrote:
> > "Jace Harker" <jharker_at_marlboro.edu> wrote in message news:<vhuhvgjqr27d83_at_corp.supernews.com>...
> >
> >>"--CELKO--" <71062.1056_at_compuserve.com> wrote in message
> >>news:c0d87ec0.0307220645.2ccab82f_at_posting.google.com...
> >
> >

[...]
>
> In the "pure" nested set, any parent has (right - left - 1) / 2 = number
> of children.
> Therefore it's easy to find out whether there are any children.
>

Yes, but it is still a bit of a hazzle to make the database understand when it should allow removal of an emp(?).

CREATE TABLE OrgChart (

        emp CHAR(10) NOT NULL PRIMARY KEY,
        boss CHAR(10) NOT NULL,
        foreign key (boss) references OrgChart
                on delete restrict

);

should be enough to prevent the situation. Using nested set I assume one would have to use triggers or some similar construct to prevent the same thing. Perhaps one could express it using a check constraint? Without given it too much thought, I assume the constraint would contain a select statement, last time I checked DB2 did not support that, perhaps other databases does?

Regards,
/Lennart

--
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Received on Mon Jul 28 2003 - 14:46:26 CDT

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