Example of adding additional branches

[masonproffitt]

From Andrea Rizzi:

In another thread we recently had a discussion on the flexibility to
"add additional branches" (originating from some parent data file) and
it would also be nice to add such kind of examples.

[masonproffitt]

From a conversation in #16: We can assume that the underlying system can handle added columns using exactly the same interface as the existing ones, but we should add a note about this assumption in case a system does not have this feature.

[ingomueller-net]

I agree that #16 is a duplicate of this one. I shall add that the system, in particular, needs to be able to produce data in a format that can be used as input of other queries. In contrast, all of the current queries produce histograms, which may be plotted and which it would not make sense to query again. (Indeed, in Presto it is quite inconvenient to produce new arrays, which I why I had opened #16.)