From: | Paul Jungwirth <pj(at)illuminatedcomputing(dot)com> |
---|---|
To: | pgsql-general(at)lists(dot)postgresql(dot)org |
Subject: | Re: Is postorder tree traversal possible with recursive CTE's? |
Date: | 2018-06-19 21:31:50 |
Message-ID: | 1e2e2542-3fbf-e419-fd9a-4e3f02421bbb@illuminatedcomputing.com |
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Lists: | pgsql-general |
On 06/19/2018 02:05 PM, Alban Hertroys wrote:
> On the more theoretical front: The question remains whether it is possible to calculate fields in post-order tree traversal. I think that would be a semantically proper way to express this type of problem and it wouldn't need the kinds of pre/post-processing that after-the-fact aggregation (like in above solution) requires. So, leaner, and probably faster.
> That implies that the SQL committee thought of the possibility in the first place though, which I'm beginning to doubt...
If this interests you, you might enjoy this StackOverflow question:
https://stackoverflow.com/questions/35956486/generate-nested-json-with-couting-in-postgresql
Briefly, how do you construct a nested JSON structure from a recursive
CTE? The only answers at that link rely on plpgsql, but of course that
is cheating. :-) I took a stab at it a couple years ago but couldn't
figure it out, and it seemed like post-order processing was exactly the
missing piece.
If anyone has any ideas I'd be intrigued to hear them!
--
Paul ~{:-)
pj(at)illuminatedcomputing(dot)com
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