Am 05/23/2017 um 06:59 PM schrieb Jeff Janes: > On Tue, May 23, 2017 at 4:03 AM, Gunnar "Nick" Bluth > <gunnar.bluth.extern@xxxxxxxxx <mailto:gunnar.bluth.extern@xxxxxxxxx>> > wrote: 8>< ----- > > Unfortunately that always uses the index scan, even at a high cutoff > where aggregation on the seq scan and then hash joining is more > appropriate. So it is very similar to view2, except that it doesn't > return the rows from "thing" which have zero corresponding rows in > thing_alias. > > ***** > Note btw. that both view1 and view2 don't return any md5 values for me, > while view3 does! > ***** > > > Because of the way I constructed the data, using the power transform of > the uniform random distribution, the early rows of the view (if sorted > by thing_id) are mostly null in the md5 column, so if you only look at > the first few screen-fulls you might not see any md5. But your view > does effectively an inner join rather than a left join, so your view > gets rid of the rows with a NULL md5. Most things don't have aliases; > of the things that do, most have 1; and some have a several. D'oh, of course! My bad... shouldn't have looked at the results with LIMIT :-/ My next best guess would involve a MatView for the aggregates... -- Gunnar "Nick" Bluth DBA ELSTER Tel: +49 911/991-4665 Mobil: +49 172/8853339
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