Re: Combining Aggregates

On 18 December 2014 at 02:48, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>
>
> David, if you can update your patch with some docs to explain the
> behaviour, it looks complete enough to think about committing it in
> early January, to allow other patches that depend upon it to stand a
> chance of getting into 9.5. (It is not yet ready, but I see it could
> be).
>
>
Sure, I've more or less added the docs from your patch. I still need to
trawl through and see if there's anywhere else that needs some additions.

> The above example is probably the best description of the need, since
> user defined aggregates must also understand this.
>
> Could we please call these "combine functions" or other? MERGE is an
> SQL Standard statement type that we will add later, so it will be
> confusing if we use the "merge" word in this context.
>
>
Ok, changed.

> David, your patch avoids creating any mergefuncs for existing
> aggregates. We would need to supply working examples for at least a
> few of the builtin aggregates, so we can test the infrastructure. We
> can add examples for all cases later.
>
>
In addition to MIN(), MAX(), BIT_AND(), BIT_OR, SUM() for floating point
types, cash and interval. I've now added combine functions for count(*) and
count(col). It seems that int8pl() is suitable for this.

Do you think it's worth adding any new functions at this stage, or is it
best to wait until there's a patch which can use these?

Regards

David Rowley