Re: contrib/tree issues
От | Oleg Bartunov |
---|---|
Тема | Re: contrib/tree issues |
Дата | |
Msg-id | Pine.GSO.4.44.0205292303370.4042-100000@ra.sai.msu.su обсуждение исходный текст |
Ответ на | Re: contrib/tree issues (Achilleus Mantzios <achill@matrix.gatewaynet.com>) |
Список | pgsql-sql |
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 ------1.11.2 (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 > > > > > > > > > ---------------------------(end of broadcast)--------------------------- > > > TIP 3: if posting/reading through Usenet, please send an appropriate > > > subscribe-nomail command to majordomo@postgresql.org so that your > > > message can get through to the mailing list cleanly > > > > > > > Regards, > > Oleg > > _____________________________________________________________ > > Oleg Bartunov, sci.researcher, hostmaster of AstroNet, > > Sternberg Astronomical Institute, Moscow University (Russia) > > Internet: oleg@sai.msu.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@sai.msu.su, http://www.sai.msu.su/~megera/ phone: +007(095)939-16-83, +007(095)939-23-83
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