Execution example::

  plugin_register sharding
  
  table_create Logs_20170415 TABLE_NO_KEY
  column_create Logs_20170415 timestamp COLUMN_SCALAR Time
  column_create Logs_20170415 price COLUMN_SCALAR UInt32
  column_create Logs_20170415 n_likes COLUMN_SCALAR UInt32
  
  table_create Logs_20170416 TABLE_NO_KEY
  column_create Logs_20170416 timestamp COLUMN_SCALAR Time
  column_create Logs_20170416 price COLUMN_SCALAR UInt32
  column_create Logs_20170416 n_likes COLUMN_SCALAR UInt32
  
  load --table Logs_20170415
  [
  {"timestamp": "2017/04/15 00:00:00", "n_likes": 2, "price": 100},
  {"timestamp": "2017/04/15 01:00:00", "n_likes": 1, "price": 100},
  {"timestamp": "2017/04/15 01:00:00", "n_likes": 2, "price": 200}
  ]
  
  load --table Logs_20170416
  [
  {"timestamp": "2017/04/16 10:00:00", "n_likes": 1, "price": 200},
  {"timestamp": "2017/04/16 11:00:00", "n_likes": 2, "price": 300},
  {"timestamp": "2017/04/16 11:00:00", "n_likes": 1, "price": 300}
  ]
  
  logical_select Logs \
    --shard_key timestamp \
    --columns[count].stage initial \
    --columns[count].type UInt32 \
    --columns[count].flags COLUMN_SCALAR \
    --columns[count].value 'window_count()' \
    --columns[count].window.group_keys price \
    --output_columns price,count
  # [
  #   [
  #     0,
  #     0.0,
  #     0.0
  #   ],
  #   [
  #     [
  #       [
  #         6
  #       ],
  #       [
  #         [
  #           "price",
  #           "UInt32"
  #         ],
  #         [
  #           "count",
  #           "UInt32"
  #         ]
  #       ],
  #       [
  #         100,
  #         2
  #       ],
  #       [
  #         100,
  #         2
  #       ],
  #       [
  #         200,
  #         2
  #       ],
  #       [
  #         200,
  #         2
  #       ],
  #       [
  #         300,
  #         2
  #       ],
  #       [
  #         300,
  #         2
  #       ]
  #     ]
  #   ]
  # ]
