On 20/12/06, Steinar H. Gunderson <sgunderson@xxxxxxxxxxx> 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.
