Its a way of representing a tree with right-left pointers in each
record (basically re-inventing a hierarchical database
in a relational model...). A good description is in Joe Celko's SQL
For Smarties book. Selection is very fast because
any node's children have node ID's between the right and left nodes of
said node, so there's no mucking about
with connect by and what not. There's a synopsis linked at the PG
Cookbook pages (http://www.brasileiro.net/postgres/cookbook),
but the cookbook seems to off-line (I think I'll offer to mirror it -
this happens frequently). There's another description at
http://www.intelligententerprise.com/001020/celko.jhtml?
_requestid=65750.
Insertion takes a fair amount of work, as you generally have to
re-arrange the node IDs when you add a record.
On Mar 29, 2004, at 12:05 PM, Jaime Casanova wrote:
>
>> Andrew,
>
>> > I used to use the connect-by patch, but have since rewritten
>> everything
>> > to use a nested set model.
>
>> Cool! You're probably the only person I know other than me using
>> nested sets
>> in a production environment.
>
>
> can you explain me what is a nested set?
>
> _________________________________________________________________
> Add photos to your messages with MSN 8. Get 2 months FREE*.
> http://join.msn.com/?page=features/featuredemail
>
>
> ---------------------------(end of
> broadcast)---------------------------
> TIP 5: Have you checked our extensive FAQ?
>
> http://www.postgresql.org/docs/faqs/FAQ.html
>
--------------------
Andrew Rawnsley
President
The Ravensfield Digital Resource Group, Ltd.
(740) 587-0114
www.ravensfield.com