Обсуждение: PK and FK relation ship

Can any one tell me when would a primary key be refered to as foreign key in
its own table.

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Shÿam Peri

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On Thu, 11 Sep 2003 shyamperi@davlin.co.in wrote:

> Can any one tell me when would a primary key be refered to as foreign key in
> its own table.
>
    Simple Trees.

    If you need a parent child relationship the simplest way of
expressing it is to have a parent columnn and store the parent key in it.
If its null it must be the root.
    Its really quite good for finding parents and children of a
record. (Children are "SELECT * from table where parent=<n.id>`;" parent
is "SELECT * from table where id=<n.parent>;")
    Could also be used for storing a linked list or double linked
list.
    Find any standard algorithims book and try and implement the lot
in a database. (Its not easy as SQL has a lot of missing features that
even C, C++ or even VB has!)

Peter Childs