On 20/12/06, Steinar H. Gunderson <[EMAIL PROTECTED]> wrote:
On Tue, Dec 19, 2006 at 11:19:39PM -0800, Brian Herlihy wrote:
> Actually, I think I answered my own question already. But I want to
> confirm - Is the GROUP BY faster because it doesn't have to sort results,
> whereas DISTINCT must produce sorted results? This wasn't clear to me from
> the documentation. If it's true, then I could save considerable time by
> using GROUP BY where I have been using DISTINCT in the past. Usually I
> simply want a count of the distinct values, and there is no need to sort
> for that.
You are right; at the moment, GROUP BY is more intelligent than DISTINCT,
even if they have to compare the same columns. This is, as always, something
that could be improved in a future release, TTBOMK.
/* Steinar */
Oh so thats why group by is nearly always quicker than distinct. I
always thought distinct was just short hand for "group by same columns
as I've just selected"
Is it actually in the sql spec to sort in a distinct or could we just
get the parser to rewrite distinct into group by and hence remove the
extra code a different way of doing it must mean.?
Peter.
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