r0 := UnboundTable: t
  col int64

r1 := Aggregate[r0]
  metrics:
    agged_struct: ReductionVectorizedUDF(func=multi_output_udf, func_args=[r0.col], input_type=[int64], return_type={'sum': int64, 'mean': float64})

Project[r1]
  sum:  StructField(r1.agged_struct, field='sum')
  mean: StructField(r1.agged_struct, field='mean')