Hannu Krosing kirjutas L, 07.12.2002 kell 02:32:
> Tom Lane kirjutas L, 07.12.2002 kell 01:46:
> > "Josh Berkus" <josh@agliodbs.com> writes:
> > > What have other Postgres users done to speed up aggregates on large
> > > tables?
> >
> > FWIW, I've implemented hashed aggregation in CVS tip.
>
> Great!
>
> This should also make it easier to implement all kinds of GROUP BY
> ROLLUP|CUBE|GROUPING SETS|() queries.
Of these only ROLLUP can be done in one scan after sort, all others
would generally require several scans without hashing.
I just noticed that we don't even have a TODO for this. I think this
would be a good TODO item.
Bruce, could you add:
* Add ROLLUP, CUBE, GROUPING SETS options to GROUP BY
They are all defined in SQL99 p.79 <group by clause>
Some more background info (from a quick Google search)
a very short overview:
http://www.neddo.com/dm3e/sql3&olap.html
more thorough guide for DB2:
http://www.student.math.uwaterloo.ca/~cs448/db2_doc/html/db2s0/frame3.htm#db2s0279
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Hannu