"`extract:timeFormat` always returns a string; there are cases where we'd like to return an integer instead, such as `:day-of-month`.
There's no simple way to do this in Druid -- Druid 0.9.0+ *does* let you combine extraction functions with `:cascade`, but we're still supporting 0.8.x.
Instead, we will perform the conversions in Clojure-land during post-processing. If we need to perform the extra post-processing step, we'll name the resulting
column `:timestamp___int`; otherwise we'll keep the name `:timestamp`."