On May 29, 2007, at 11:58 , psql-novice@netzach.co.il wrote:
> I have a table which looks like this:
>
> id info parentid
> 0 <God> 0
> 1 Adam 0
> 2 Cain 1
> 3 Abel 1
> 4 Seth 1
> 5 Enosh 4
> ....
>
>
>
> I am looking for a fast and efficient way of finding ALL the
> descendents
> of any particular node, to unlimited depth.
>
> Is there a standard database trick for doing this efficiently ?
> Writing
> a recursive function would be extremely inefficient for repeated
> queries.
What you've got there is often called an adjacency list. Check out
the connect_by function in the tablefunc contrib module (contrib/
tablefunc). You might also want to google for SQL nested sets to find
an alternative method of doing handling trees.
Michael Glaesemann
grzm seespotcode net