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@xxxxxxxxxxxxxxxxxxxxxxxx
