On Sep 23, 2004, at 6:36 PM, Stephan Szabo wrote:
On Thu, 23 Sep 2004, Matthew Hixson wrote:
I have a categories table that contains a FK to another category in the
same table, creating a hierarchy. At the very top is this row:
category_id | name | description | parent_id -------------+------+-------------------------+----------- 1 | ROOT | The top level category. | 0
There is no record with category_id 0 because ROOT is at the top of the
tree. I'd like to set up a constraint on this table so that every
category has to have a parent_id and it would be impossible to delete a
category if it had subcategories. The problem is that this root
category violates that constraint. Is there a way to setup the
constraint so that it constrains every record except for forcing the
root category to point at a real parent category?
Well, to simply have the root category not error, you could use NULL for
the parent_id if you're using a foreign key.
Okay, now I just feel silly. For some reason I was thinking that the parent id couldn't be NULL either.
Thanks, this is exactly what I needed.
-M@
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