Execution example::

  select Users --output_columns name,memo,_score --match_columns "memo * 10" --query "memo:@groonga OR memo:@mroonga OR memo:@user" --sort_keys -_score
  # [
  #   [
  #     0, 
  #     1337566253.89858, 
  #     0.000355720520019531
  #   ], 
  #   [
  #     [
  #       [
  #         5
  #       ], 
  #       [
  #         [
  #           "name", 
  #           "ShortText"
  #         ], 
  #         [
  #           "memo", 
  #           "ShortText"
  #         ], 
  #         [
  #           "_score", 
  #           "Int32"
  #         ]
  #       ], 
  #       [
  #         "Tobby", 
  #         "groonga and mroonga user. mroonga is ...", 
  #         4
  #       ], 
  #       [
  #         "Alice", 
  #         "groonga user", 
  #         2
  #       ], 
  #       [
  #         "Alisa", 
  #         "mroonga user", 
  #         2
  #       ], 
  #       [
  #         "Bob", 
  #         "rroonga user", 
  #         1
  #       ], 
  #       [
  #         "Tom", 
  #         "nroonga user", 
  #         1
  #       ]
  #     ]
  #   ]
  # ]
