Re: Two Index Questions

Josh Berkus wrote:
> Bruno, Tom,
> 
> > Typo. I meant to say columns. The issue is that max doesn't use an index,
> > but if there are a lot of different values of G for a given A, B and C,
> > it may be better to use an index then to search through the applicable
> > rows to find the maximum.
> 
> That's odd ... you're correct.   Tom, why doesn't MAX() use an index?   I 
> understand why indexes are generally useless for SUM(), AVG, and COUNT, but 
> it seems that MAX() and MIN() should *always* use an index.

Index access methods don't know about aggregates, and our type system
makes such linkage difficult.  The FAQ does have:    However, <SMALL>LIMIT</SMALL> combined with <SMALL>ORDER
BY</SMALL>   often will use an index because only a small portion of the table    is returned.  In fact, though MAX()
andMIN() don't use indexes,    it is possible to retrieve such values using an index with ORDER BY    and LIMIT:<PRE>
SELECT col    FROM tab    ORDER BY col [ DESC ]    LIMIT 1</PRE>
 

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