On Oct 20, 2007, at 7:33 , Merlin Moncure wrote:
On 10/19/07, Richard Broersma Jr <rabroersma@xxxxxxxxx> wrote:
Is it possible to constraint both the LEFT and RIGHT fields of a
record to use the same index? I am looking for a way to ensure
for all LEFTs and RIGHTs in a table, that is it is impossible for
any LEFT or RIGHT to have to same value.
I found the celko's approach to be not very scalable...if you do any
inserts at all into the tree the table will thrash terribly. Have you
eliminated other approaches, such as arrays, ltree, etc?
I believe it's a trade off: if you're doing a lot of aggregate work
and not very many updates, nested sets works very well: adjacency
lists aren't as good for this because of the necessity of following
the hierarchy from parent to child. If your hierarchy is updated
frequently, yes, you'll have a lot of thrashing as everything above
and to the left of the update must be updated as well. AFAIK, there
isn't currently a single best solution for representing trees in SQL.
Michael Glaesemann
grzm seespotcode net
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