Hi Robert, Oh, I do care about these columns. But by using an group by on the key columns, I cannot select the columns as they are. Otherwise you get an error message. So I have to use an aggregate functionlike min().
Best... Uwe On 19 April 2011 10:24, Robert Klemme <shortcut...@googlemail.com> wrote: > On Mon, Apr 18, 2011 at 7:13 PM, Uwe Bartels <uwe.bart...@gmail.com> > wrote: > > the aggregate function I was talking about is the function I need to use > for > > the non-group by columns like min() in my example. > > There are of course several function to choose from, and I wanted to know > > which causes as less as possible resources. > > If you do not care about the output of the non key columns, why do you > include them in the query at all? That would certainly be the > cheapest option. > > If you need _any_ column value you can use a constant. > > rklemme=> select * from t1; > k | v > ---+--- > 0 | 0 > 0 | 1 > 1 | 2 > 1 | 3 > 2 | 4 > 2 | 5 > 3 | 6 > 3 | 7 > 4 | 8 > 4 | 9 > (10 rows) > > rklemme=> select k, 99 as v from t1 group by k order by k; > k | v > ---+---- > 0 | 99 > 1 | 99 > 2 | 99 > 3 | 99 > 4 | 99 > (5 rows) > > rklemme=> > > Greetings from Paderborn > > robert > > -- > remember.guy do |as, often| as.you_can - without end > http://blog.rubybestpractices.com/ >
