Execution example::

  plugin_register functions/string \
  logical_select \
    --logical_table Entries \
    --shard_key created_at \
    --limit 0 \
    --output_columns _id \
    --drilldowns[tag].keys tag \
    --drilldowns[tag].columns[tag_length].stage initial \
    --drilldowns[tag].columns[tag_length].type UInt32 \
    --drilldowns[tag].columns[tag_length].value 'string_length(_key)' \
    --drilldowns[tag].output_columns _key,tag_length
  # [[0,1337566253.89858,0.000355720520019531],true]
