On Mon, 31 Jan 2005 14:40:08 -0500, Tom Lane <[EMAIL PROTECTED]> wrote:
>Manfred Koizar <[EMAIL PROTECTED]> writes:
>> That's not what I meant. I tried to say that if we have a GROUP BY
>> several columns and one of these columns alone has more than N/10
>> distinct values, there's no way to get less than that many groups.
>
>Oh, I see, you want a "max" calculation in there too. Seems reasonable.
>Any objections?
Yes. :-( What I said is only true in the absence of any WHERE clause
(or join). Otherwise the same cross-column correlation issues you tried
to work around with the N/10 clamping might come back through the
backdoor. I'm not sure whether coding for such a narrow use case is
worth the trouble. Forget my idea.
Servus
Manfred
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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
