columns {
  name: "column0"
  type {
    type_id: UINT64
  }
}
columns {
  name: "column1"
  type {
    optional_type {
      item {
        type_id: UINT64
      }
    }
  }
}
columns {
  name: "column2"
  type {
    optional_type {
      item {
        type_id: UINT32
      }
    }
  }
}
rows {
  items {
    uint64_value: 3
  }
  items {
    uint64_value: 30
  }
  items {
    uint32_value: 10
  }
}
