columns {
  name: "quantile"
  type {
    type_id: DOUBLE
  }
}
columns {
  name: "key_q"
  type {
    optional_type {
      item {
        type_id: DOUBLE
      }
    }
  }
}
columns {
  name: "count"
  type {
    type_id: UINT64
  }
}
rows {
  items {
    double_value: 10
  }
  items {
    double_value: 20
  }
  items {
    uint64_value: 4
  }
}
