nuno-faria commented on PR #17058:
URL: https://github.com/apache/datafusion/pull/17058#issuecomment-3171931826
Thanks @berkaysynnada for the pointers. I did a little more digging and
found that the `get_finer_aggregate_exprs_requirement` function returns a
different value for `string_agg` and `array_agg`. The source of the difference
is that `AggregateUDFImpl::reverse_expr` is not defined for `string_agg`. This
means the `SortExec` will not be created for `string_agg`, and that is still
true in the main branch of datafusion.
```
# string_agg
| physical_plan after CombinePartialFinalAggregate |
OutputRequirementExec: order_by=[], dist_by=Unspecified
| |
AggregateExec: mode=Single, gby=[], aggr=[string_agg(t.k,Utf8(",")) ORDER BY
[t.v ASC NULLS LAST]]
| |
DataSourceExec: partitions=1, partition_sizes=[1]
| |
| physical_plan after EnforceSorting | SAME TEXT AS
ABOVE
# array_agg
| physical_plan after CombinePartialFinalAggregate |
OutputRequirementExec: order_by=[], dist_by=Unspecified
| |
AggregateExec: mode=Single, gby=[], aggr=[array_agg(t.k) ORDER BY [t.v ASC
NULLS LAST]]
| |
DataSourceExec: partitions=1, partition_sizes=[1]
| |
| physical_plan after EnforceSorting |
OutputRequirementExec: order_by=[], dist_by=Unspecified
| |
AggregateExec: mode=Single, gby=[], aggr=[array_agg(t.k) ORDER BY [t.v ASC
NULLS LAST]]
| | SortExec:
expr=[v@1 ASC NULLS LAST], preserve_partitioning=[false]
| |
DataSourceExec: partitions=1, partition_sizes=[1]
```
The fix is to simply implement `AggregateUDFImpl::reverse_expr` for
`StringAgg`. @alamb @findepi what do you think of this approach? With it there
is no need cherry pick a new feature into `49.0.1`.
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