Derivative should calculate rate between each point if no group by time is given

[pauldix]

Currently, the derivative will calculate between the very first and very last point if no group by time is given. I think what's in the title is what most people actually want.

[stapelberg]

I think this is a duplicate of #334 :)

I’d love to beta-test this feature. A lot of my planned monitoring is blocked on having this.

[jvshahid]

They aren't quite the same. This story is about the derivatives when there's no group by time() clause in the query. #334 is about derivatives when there is a group by time() clause.

[johnarnold]

Update?

[beckettsean]

@jwilder does DERIVATIVE already do this?

[jwilder]

@beckettsean Yes