alamb commented on code in PR #7129:
URL: https://github.com/apache/arrow-datafusion/pull/7129#discussion_r1279180964
##########
datafusion/core/tests/sqllogictests/test_files/groupby.slt:
##########
@@ -2689,13 +2703,12 @@ SortPreservingMergeExec: [country@0 ASC NULLS LAST]
--SortExec: expr=[country@0 ASC NULLS LAST]
----ProjectionExec: expr=[country@0 as country,
FIRST_VALUE(sales_global.amount) ORDER BY [sales_global.ts ASC NULLS LAST]@1 as
fv1, LAST_VALUE(sales_global.amount) ORDER BY [sales_global.ts ASC NULLS
LAST]@2 as fv2]
------AggregateExec: mode=FinalPartitioned, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)]
---------SortExec: expr=[ts@1 ASC NULLS LAST]
-----------CoalesceBatchesExec: target_batch_size=8192
-------------RepartitionExec: partitioning=Hash([country@0], 8),
input_partitions=8
---------------AggregateExec: mode=Partial, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)],
ordering_mode=None
-----------------SortExec: expr=[ts@1 ASC NULLS LAST]
-------------------RepartitionExec: partitioning=RoundRobinBatch(8),
input_partitions=1
---------------------MemoryExec: partitions=1, partition_sizes=[1]
+--------CoalesceBatchesExec: target_batch_size=8192
+----------RepartitionExec: partitioning=Hash([country@0], 8),
input_partitions=8
+------------AggregateExec: mode=Partial, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)]
Review Comment:
I am not sure this new plan is correct either as the data is not necessarily
sorted for the final grouping . The old plan also seems wrong.
My reasoning is that for an aggregate like this:
```
FIRST_VALUE(amount ORDER BY ts ASC)
```
the input to the group operator has to be sorted on `ts`.
However, I don't see how the order by `ts` is preserved after the
`AggregateExec: mode=Partial` first grouping phase
```shell
------AggregateExec: mode=FinalPartitioned, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)]
** I think the order by `ts` is not preserved here, so the data is not
ordered by ts for the final grouping **
------------AggregateExec: mode=Partial, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)]
```
Maybe the right solution would be to do a single phase grouping when any of
the aggregates have an `ORDER BY` clause
```
AggregateExec: mode=Final, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)] ** no
partial group by
SortExec: expr=[ts@1 ASC NULLS LAST]
RepartitionExec: partitioning=RoundRobinBatch(8), input_partitions=1
MemoryExec: partitions=1, partition_sizes=[1]
```
🤔
##########
datafusion/core/tests/sqllogictests/test_files/groupby.slt:
##########
@@ -2689,13 +2703,12 @@ SortPreservingMergeExec: [country@0 ASC NULLS LAST]
--SortExec: expr=[country@0 ASC NULLS LAST]
----ProjectionExec: expr=[country@0 as country,
FIRST_VALUE(sales_global.amount) ORDER BY [sales_global.ts ASC NULLS LAST]@1 as
fv1, LAST_VALUE(sales_global.amount) ORDER BY [sales_global.ts ASC NULLS
LAST]@2 as fv2]
------AggregateExec: mode=FinalPartitioned, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)]
---------SortExec: expr=[ts@1 ASC NULLS LAST]
-----------CoalesceBatchesExec: target_batch_size=8192
-------------RepartitionExec: partitioning=Hash([country@0], 8),
input_partitions=8
---------------AggregateExec: mode=Partial, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)],
ordering_mode=None
-----------------SortExec: expr=[ts@1 ASC NULLS LAST]
-------------------RepartitionExec: partitioning=RoundRobinBatch(8),
input_partitions=1
---------------------MemoryExec: partitions=1, partition_sizes=[1]
+--------CoalesceBatchesExec: target_batch_size=8192
+----------RepartitionExec: partitioning=Hash([country@0], 8),
input_partitions=8
+------------AggregateExec: mode=Partial, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)]
Review Comment:
I am not sure this new plan is correct either as the data is not necessarily
sorted for the final grouping . The old plan also seems wrong.
My reasoning is that for an aggregate like this:
```
FIRST_VALUE(amount ORDER BY ts ASC)
```
the input to the group operator has to be sorted on `ts`.
However, I don't see how the order by `ts` is preserved after the
`AggregateExec: mode=Partial` first grouping phase
```shell
------AggregateExec: mode=FinalPartitioned, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)]
** I think the order by `ts` is not preserved here, so the data is not
ordered by ts for the final grouping **
------------AggregateExec: mode=Partial, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)]
```
Maybe the right solution would be to do a single phase grouping when any of
the aggregates have an `ORDER BY` clause
```
AggregateExec: mode=Final, gby=[country@0 as country],
aggr=[FIRST_VALUE(sales_global.amount), LAST_VALUE(sales_global.amount)] ** no
partial group by
SortExec: expr=[ts@1 ASC NULLS LAST]
RepartitionExec: partitioning=RoundRobinBatch(8), input_partitions=1
MemoryExec: partitions=1, partition_sizes=[1]
```
🤔
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