Re: onlyvalue aggregate (was: First Aggregate Funtion?)

On 11/2/15 9:32 AM, Dean Rasheed wrote:
> On 28 October 2015 at 16:50, Marko Tiikkaja <marko(at)joh(dot)to> wrote:
>> Here's a patch for the aggregate function outlined by Corey Huinker in
>> CADkLM=foA_oC_Ri23F9PbfLnfwXFbC3Lt8bBzRu3=CB77G9_qw(at)mail(dot)gmail(dot)com .
>
> +1. I've wanted something like this a few times. Of the names
> suggested so far, I think I prefer "single_value", and yes I think it
> should work with NULLs.

This was actually a last-minute design change I made before submitting
the patch. The two times I've previously written this aggregate both
accepted NULLs and only enforced that there must not be more than one
non-NULL value, but that's only because I was thinking about the "poor
man's FILTER" case, which is obsolete since version 9.4. The reason I
changed in this version is that accepting NULLs can also hide bugs, and
it's (usually) easy to filter them out with FILTER.

Did you have some specific use case in mind where accepting NULLs would
be beneficial?

.m