Execution example::

  select --table Comments --query hash_tags:@groonga --output_columns posted_by.name,comment --drilldown posted_by
  # [
  #   [
  #     0, 
  #     1337566253.89858, 
  #     0.000355720520019531
  #   ], 
  #   [
  #     [
  #       [
  #         2
  #       ], 
  #       [
  #         [
  #           "posted_by.name", 
  #           "ShortText"
  #         ], 
  #         [
  #           "comment", 
  #           "ShortText"
  #         ]
  #       ], 
  #       [
  #         "Bob", 
  #         "I've just used 'Try-Groonga' now! #groonga"
  #       ], 
  #       [
  #         "Bob", 
  #         "I'm come at city of New York for development camp! #groonga #travel"
  #       ]
  #     ], 
  #     [
  #       [
  #         1
  #       ], 
  #       [
  #         [
  #           "_key", 
  #           "ShortText"
  #         ], 
  #         [
  #           "_nsubrecs", 
  #           "Int32"
  #         ]
  #       ], 
  #       [
  #         "bob", 
  #         2
  #       ]
  #     ]
  #   ]
  # ]
