>>>>> "Tomas" == Tomas Vondra <t...@fuzzy.cz> writes:
>> It's not one sort per grouping set, it's the minimal number of
>> sorts needed to express the result as a union of ROLLUP
>> clauses. The planner code will (I believe) always find the
>> smallest number of sorts needed.
Tomas> You're probably right. Although when doing GROUP BY CUBE
Tomas> (a,b,c,a) I get one more ChainAggregate than with
Tomas> CUBE(a,b,c). and we seem to compute all the aggregates
Tomas> twice. Not sure if we need to address this though, because
Tomas> it's mostly user's fault.
Hm. Yeah, you're right that the number of sorts is not optimal there.
We can look into that.
As for computing it all twice, there's currently no attempt to
optimize multiple identical grouping sets into multiple projections of
a single grouping set result. CUBE(a,b,c,a) has twice as many grouping
sets as CUBE(a,b,c) does, even though all the extra ones are duplicates.
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