On Fri, Sep 19, 2014 at 4:45 AM, Andrew Gierth <and...@tao11.riddles.org.uk> wrote: > GroupAggregate (cost=1122.39..1197.48 rows=9 width=8) > Group Key: two, four > Group Key: two > Group Key: ()
> "Grouping Sets": [ > ["two", "four"], > ["two"], > [] +1 looks good to me. > (yaml format) > Grouping Sets: > - - "two" > - "four" > - - "two" > - Now this is weird. But is anyone actually using YAML output format, or was it implemented simply "because we can"? > Marti> Do you think it would be reasonable to normalize single-set > Marti> grouping sets into a normal GROUP BY? > It's certainly possible, though it would seem somewhat odd to write > queries that way. The reason I bring this up is that queries are frequently dynamically generated by programs. Coders are unlikely to special-case SQL generation when there's just a single grouping set. And that's the power of relational databases: the optimization work is done in the database pretty much transparently to the coder (when it works, that is). > would you want the original syntax preserved in views Doesn't matter IMO. > Marti> I'd expect GROUP BY () to be fully equivalent to having no > Marti> GROUP BY clause, but there's a difference in explain > Marti> output. The former displays "Grouping Sets: ()" which is odd, > Marti> since none of the grouping set keywords were used. > That's an implementation artifact, in the sense that we preserve the > fact that GROUP BY () was used by using an empty grouping set. Is it > a problem, really, that it shows up that way in explain? No, not really a problem. :) Regards, Marti -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
