Peter Eisentraut <pete...@gmx.net> writes: > On tis, 2010-06-08 at 09:59 +0900, Hitoshi Harada wrote: >> In addition, what if y is implicitly a constant? For example, >> >> SELECT x, y FROM tab2 WHERE y = a AND a = 5 GROUP BY x;
> Yes, as I said, my implementation is incomplete in the sense that it > only recognizes some functional dependencies. To recognize the sort of > thing you show, you would need some kind of complex deduction or proof > engine, and that doesn't seem worthwhile, at least for me, at this > point. The question is why bother to recognize *any* cases of this form. I find it really semantically ugly to have the parser effectively doing one deduction of this form when the main engine for that type of deduction is elsewhere; so unless there is a really good argument why we have to do this case (and NOT "it was pretty easy"), I don't want to do it. As far as I recall, at least 99% of the user requests for this type of behavior, maybe 100%, would be satisfied by recognizing the group-by-primary-key case. So I think we should do that and be happy. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers