On Apr 18, 2011, at 1:13 PM, Uwe Bartels <uwe.bartels@gmail.com> wrote: > Hi Robert, > > thanks for your answer. > 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.
Oh, I see. min() is probably as good as anything. You could also create a custom aggregate that just always returns its first input. I've occasionally wished we had such a thing as a built-in.
I've once done "single" grouping function - it checks that all it's input values are equal (non-null ones) and returns the value or raises an error if there are two different values.
