alamb commented on code in PR #10913:
URL: https://github.com/apache/datafusion/pull/10913#discussion_r1641319524
##########
datafusion/sqllogictest/test_files/joins.slt:
##########
@@ -1382,18 +1382,17 @@ physical_plan
02)--AggregateExec: mode=Final, gby=[], aggr=[COUNT(alias1)]
03)----CoalescePartitionsExec
04)------AggregateExec: mode=Partial, gby=[], aggr=[COUNT(alias1)]
-05)--------AggregateExec: mode=FinalPartitioned, gby=[alias1@0 as alias1],
aggr=[]
-06)----------AggregateExec: mode=Partial, gby=[t1_id@0 as alias1], aggr=[]
-07)------------CoalesceBatchesExec: target_batch_size=2
-08)--------------HashJoinExec: mode=Partitioned, join_type=Inner,
on=[(t1_id@0, t2_id@0)], projection=[t1_id@0]
-09)----------------CoalesceBatchesExec: target_batch_size=2
-10)------------------RepartitionExec: partitioning=Hash([t1_id@0], 2),
input_partitions=2
-11)--------------------RepartitionExec: partitioning=RoundRobinBatch(2),
input_partitions=1
-12)----------------------MemoryExec: partitions=1, partition_sizes=[1]
-13)----------------CoalesceBatchesExec: target_batch_size=2
-14)------------------RepartitionExec: partitioning=Hash([t2_id@0], 2),
input_partitions=2
-15)--------------------RepartitionExec: partitioning=RoundRobinBatch(2),
input_partitions=1
-16)----------------------MemoryExec: partitions=1, partition_sizes=[1]
+05)--------AggregateExec: mode=SinglePartitioned, gby=[t1_id@0 as alias1],
aggr=[]
Review Comment:
I agree this plan looks better and correct
##########
datafusion/core/src/physical_optimizer/combine_partial_final_agg.rs:
##########
@@ -144,8 +144,12 @@ fn can_combine(final_agg: GroupExprsRef, partial_agg:
GroupExprsRef) -> bool {
let (input_group_by, input_aggr_expr, input_filter_expr) =
normalize_group_exprs(partial_agg);
- final_group_by.eq(&input_group_by)
Review Comment:
I am not sure that just checking the length of the group bys is sufficient
-- I think logically they must be the same.
It seems like the reason these weren't combined
```
05)--------AggregateExec: mode=FinalPartitioned, gby=[alias1@0 as alias1],
aggr=[]
06)----------AggregateExec: mode=Partial, gby=[t1_id@0 as alias1], aggr=[]
```
Is becase of aliasing the exprs didn't match exactly -- `t1_id@0 as alias1`
didn't match `alias1@0 as alias1` even though I think they are logically
equivalent
So for example, if we ever made the following plan (with actually different
grouping expressions) after this change the code would incorrectly collapse them
```
05)--------AggregateExec: mode=FinalPartitioned, gby=[alias1 / 2 as alias1],
aggr=[]
06)----------AggregateExec: mode=Partial, gby=[t1_id@0 as alias1], aggr=[]
```
However, I am not sure that such a plan would be valid 🤔
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