Example produces incorrect results

[andygrove]

The tips.py runs a grouping query but the result set has duplicate keys:

0    Male     No  0.160669
1  Female    Yes  0.182150
      sex smoker   tip_pct
0  Female     No  0.156921
1    Male    Yes  0.152771

Debug logging:

Planning select sex, smoker, avg(tip/total_bill) as tip_pct from tips group by sex, smoker
Query stage #0:
RayShuffleWriterExec(stage_id=0, output_partitioning=Hash([Column { name: "sex", index: 0 }, Column { name: "smoker", index: 1 }], 2))
  AggregateExec: mode=Partial, gby=[sex@2 as sex, smoker@3 as smoker], aggr=[AVG(tips.tip / tips.total_bill)]
    ParquetExec: limit=None, partitions={1 group: [[home/andy/git/personal/ray-sql/examples/tips.parquet]]}, projection=[total_bill, tip, sex, smoker]

Query stage #1:
CoalescePartitionsExec
  ProjectionExec: expr=[sex@0 as sex, smoker@1 as smoker, AVG(tips.tip / tips.total_bill)@2 as tip_pct]
    AggregateExec: mode=FinalPartitioned, gby=[sex@0 as sex, smoker@1 as smoker], aggr=[AVG(tips.tip / tips.total_bill)]
      CoalesceBatchesExec: target_batch_size=16384
        RayShuffleReaderExec(stage_id=0, input_partitioning=Hash([Column { name: "sex", index: 0 }, Column { name: "smoker", index: 1 }], 2))

Scheduling query stage #0 with 1 input partitions and 2 output partitions
Forcing reduce stage concurrency from 2 to 1
Scheduling query stage #1 with 1 input partitions and 1 output partitions
      sex smoker   tip_pct
0    Male     No  0.160669
1  Female    Yes  0.182150
      sex smoker   tip_pct
0  Female     No  0.156921
1    Male    Yes  0.152771