Execution example::

  > select --table Site --limit 0 --drilldown country --drilldown_sortby _nsubrecs
  [[0,1317212755.09777,0.000284575],[[[9],[["_id","UInt32"],["_key","ShortText"],["title","ShortText"],["location","WGS84GeoPoint"],["links","Site"],["link","Site"],["domain","SiteDomain"],["country","SiteCountry"]]],[[5],[["_key","ShortText"],["_nsubrecs","Int32"]],["brazil",1],["korea",1],["usa",2],["china",2],["japan",3]]]]