columns {
  name: "nation"
  type {
    type_id: STRING
  }
}
columns {
  name: "o_year"
  type {
    optional_type {
      item {
        type_id: UINT16
      }
    }
  }
}
columns {
  name: "sum_profit"
  type {
    type_id: DOUBLE
  }
}
