On 14 Jun 2005, at 17:52, [EMAIL PROTECTED] wrote:
My suggestion, lame as it is, would be to use a 0 (zero) in place
of the
NULL value. That way, you always have a valid entry for PARENT_ID,
you can
still identify the tops of the trees (parent_id=0) and you have gotten
around the only-one-parent-entry-can-be-null trap.
Because of the cascade deletion setting, it will not allow inserts of
any record where a record with the parent ID does not exist because
the new child record will be deleted immediately in order to satisfy
the constraint. As far as I'm aware this is exactly the kind of thing
that null vales are for - for example a constraint where the action
is set_null instead of cascade would quite correctly set the
parent_id to null, leaving an unowned child. What I need is a cascade
on delete that allows null values (on the basis that null != null
because neither is a value). Am I just fantasizing?
Marcus
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Marcus Bointon
Synchromedia Limited: Putting you in the picture
[EMAIL PROTECTED] | http://www.synchromedia.co.uk
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