It’s not powerful enough to do a Cartesian join (yet?). Most you can do is scan once over a big dataset.

Hmm. I wonder if an "index only" query charges for the scan of the index, or a full table scan.

AFAICT, there is no indexing. It appears to just scan the logs as necessary. Maybe indexing will come later.

Bigquery has a cool function like this where it will tell you the cost of the query before you run it.