Execution example::

  table_create PowerSetDrilldownMemos TABLE_HASH_KEY ShortText
  # [[0,1337566253.89858,0.000355720520019531],true]
  column_create PowerSetDrilldownMemos tags COLUMN_VECTOR ShortText
  # [[0,1337566253.89858,0.000355720520019531],true]
  load --table PowerSetDrilldownMemos
  [
  {"_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 PowerSetDrilldownMemos \
    --drilldowns[tags].keys tags \
    --drilldowns[tags].key_vector_expansion POWER_SET \
    --drilldowns[tags].columns[power_set].stage initial \
    --drilldowns[tags].columns[power_set].value _key \
    --drilldowns[tags].columns[power_set].flags COLUMN_VECTOR \
    --drilldowns[tags].sort_keys 'power_set' \
    --drilldowns[tags].output_columns 'power_set, _nsubrecs' \
    --limit 0
  # [
  #   [
  #     0,
  #     1337566253.89858,
  #     0.000355720520019531
  #   ],
  #   [
  #     [
  #       [
  #         4
  #       ],
  #       [
  #         [
  #           "_id",
  #           "UInt32"
  #         ],
  #         [
  #           "_key",
  #           "ShortText"
  #         ],
  #         [
  #           "tags",
  #           "ShortText"
  #         ]
  #       ]
  #     ],
  #     {
  #       "tags": [
  #         [
  #           7
  #         ],
  #         [
  #           [
  #             "power_set",
  #             "Text"
  #           ],
  #           [
  #             "_nsubrecs",
  #             "Int32"
  #           ]
  #         ],
  #         [
  #           [
  #             "Groonga"
  #           ],
  #           4
  #         ],
  #         [
  #           [
  #             "Mroonga"
  #           ],
  #           2
  #         ],
  #         [
  #           [
  #             "PGroonga"
  #           ],
  #           2
  #         ],
  #         [
  #           [
  #             "Groonga",
  #             "Mroonga"
  #           ],
  #           2
  #         ],
  #         [
  #           [
  #             "Groonga",
  #             "PGroonga"
  #           ],
  #           2
  #         ],
  #         [
  #           [
  #             "Mroonga",
  #             "PGroonga"
  #           ],
  #           1
  #         ],
  #         [
  #           [
  #             "Groonga",
  #             "Mroonga",
  #             "PGroonga"
  #           ],
  #           1
  #         ]
  #       ]
  #     }
  #   ]
  # ]
