Execution example::

  plugin_register functions/string
  # [[0,1337566253.89858,0.000355720520019531],true]
  select \
    --table Memos \
    --filter 'in_records(Conditions, \
                         user,                 "@", "user_pattern", \
                         tag,                 "==", "tag", \
                         string_length(_key), "<=", "max_length")' \
    --sort_by _id \
    --output_columns _key,user,tag
  # [
  #   [
  #     0,
  #     1337566253.89858,
  #     0.000355720520019531
  #   ],
  #   [
  #     [
  #       [
  #         2
  #       ],
  #       [
  #         [
  #           "_key",
  #           "ShortText"
  #         ],
  #         [
  #           "user",
  #           "ShortText"
  #         ],
  #         [
  #           "tag",
  #           "Tags"
  #         ]
  #       ],
  #       [
  #         "Groonga is fast",
  #         "alice",
  #         "groonga"
  #       ],
  #       [
  #         "Droonga is fast",
  #         "david",
  #         "droonga"
  #       ]
  #     ]
  #   ]
  # ]
