Execution example::

  table_create NoneExpantionDrilldownMemos TABLE_HASH_KEY ShortText
  # [[0, 1337566253.89858, 0.000355720520019531], true]
  column_create NoneExpantionDrilldownMemos tags COLUMN_VECTOR ShortText
  # [[0, 1337566253.89858, 0.000355720520019531], true]
  load --table NoneExpantionDrilldownMemos
  [
  {"_key": "Groonga is fast!", "tags": ["Groonga"]},
  {"_key": "Mroonga uses Groonga!", "tags": ["Groonga", "Mroonga"]},
  {"_key": "PGroonga uses Groonga!", "tags": ["Groonga", "PGroonga"]},
  {"_key": "Mroonga and PGroonga are Groonga family", "tags": ["Groonga", "Mroonga", "PGroonga"]}
  ]
  # [[0, 1337566253.89858, 0.000355720520019531], 4]
  select NoneExpantionDrilldownMemos \
    --drilldowns[tags].keys tags \
    --drilldowns[tags].key_vector_expansion NONE \
    --drilldowns[tags].columns[none_expantion].stage initial \
    --drilldowns[tags].columns[none_expantion].value _key \
    --drilldowns[tags].columns[none_expantion].flags COLUMN_VECTOR \
    --drilldowns[tags].sort_keys 'none_expantion' \
    --drilldowns[tags].output_columns 'none_expantion, _nsubrecs' \
    --limit 0
  # [
  #   [
  #     0, 
  #     1337566253.89858, 
  #     0.000355720520019531
  #   ], 
  #   [
  #     [
  #       [
  #         4
  #       ], 
  #       [
  #         [
  #           "_id", 
  #           "UInt32"
  #         ], 
  #         [
  #           "_key", 
  #           "ShortText"
  #         ], 
  #         [
  #           "tags", 
  #           "ShortText"
  #         ]
  #       ]
  #     ], 
  #     {
  #       "tags": [
  #         [
  #           3
  #         ], 
  #         [
  #           [
  #             "none_expantion", 
  #             "Text"
  #           ], 
  #           [
  #             "_nsubrecs", 
  #             "Int32"
  #           ]
  #         ], 
  #         [
  #           [
  #             "Groonga"
  #           ], 
  #           4
  #         ], 
  #         [
  #           [
  #             "Mroonga"
  #           ], 
  #           2
  #         ], 
  #         [
  #           [
  #             "PGroonga"
  #           ], 
  #           2
  #         ]
  #       ]
  #     }
  #   ]
  # ]
