On 6/8/10 5:21 PM +0300, Tom Lane wrote:
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.
+1
Regards,
Marko Tiikkaja
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