Re: contrib/tree issues

On Wed, 29 May 2002, Achilleus Mantzios wrote:

> On Wed, 29 May 2002, Oleg Bartunov wrote:
>
> > > How can we find "maximum" direct child of a node?
> > >
> > > dynatree=#
> > >
> > > Now we find the children of '1' of level 2:
> > >
> > > dynatree=# SELECT node from achtree where node <* '1.*.0';
> > > node
> > > ------
> > > 1.1
> > > 1.2
> > > (2 rows)
> > >
> > > dynatree=#
> > >
> > > Now if we want to insert another level 2 child of '1',
> > > how can we get the current maximum value of level 2 children of node '1'??
> > > (in this case 2), so that we can insert '1.3' to the table???
> >
> >
> > Just use functions entree_next(entree), bitree_next(bitree) -
> > return next free node.
>
> Ok, entree_next(1.2) is fine, but how can we know this particular
> 1.2
> ^
> ??

tree=# select * from tree where node <* '1.*.0';
node
------
1.1
1.2
(2 rows)

tree=# select entree_next(node) from tree where node <* '1.*.0' order by node desc limit 1;
entree_next
-------------
1.3
(1 row)

>
> Think of a sequence for example that increments itself.
>
> Now, if we have a unique index on a entree column, how can we guarantie
> the next one will be the previous max child + 1??
>
> >
> >
> >
> >
> > >
> > > Also, i want to ask if somebody has extended postgresql's jdbc
> > > implemantation to include support for bitrees,entrees.
> > >
> > > One maybe slow solution for both of the above would be to
> > > be able to cast e.g. entree to text, so that
> > >
> > > a) taking the lexicographically maximum bitree value would give the
> > > maximum current child, and
> > > b) java intergration would be trivial through java.lang.String.
> > >
> > > Thanx
> > >
> > >
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> > >
> >
> > Regards,
> > Oleg
> > _____________________________________________________________
> > Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
> > Sternberg Astronomical Institute, Moscow University (Russia)
> > Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
> > phone: +007(095)939-16-83, +007(095)939-23-83
> >
>
>

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83