alamb commented on code in PR #9991:
URL: https://github.com/apache/arrow-datafusion/pull/9991#discussion_r1559893156
##########
datafusion/sqllogictest/test_files/group_by.slt:
##########
@@ -2129,41 +2129,11 @@ query III
1 2 1550
1 3 2175
-
-# test_source_sorted_groupby2
-# If ordering is not important for the aggregation function, we should ignore
the ordering requirement. Hence
-# "ORDER BY a DESC" should have no effect.
-query TT
-EXPLAIN SELECT a, d,
- SUM(c ORDER BY a DESC) as summation1
- FROM annotated_data_infinite2
- GROUP BY d, a
-----
-logical_plan
-Projection: annotated_data_infinite2.a, annotated_data_infinite2.d,
SUM(annotated_data_infinite2.c) ORDER BY [annotated_data_infinite2.a DESC NULLS
FIRST] AS summation1
---Aggregate: groupBy=[[annotated_data_infinite2.d,
annotated_data_infinite2.a]], aggr=[[SUM(CAST(annotated_data_infinite2.c AS
Int64)) ORDER BY [annotated_data_infinite2.a DESC NULLS FIRST]]]
-----TableScan: annotated_data_infinite2 projection=[a, c, d]
-physical_plan
-ProjectionExec: expr=[a@1 as a, d@0 as d, SUM(annotated_data_infinite2.c)
ORDER BY [annotated_data_infinite2.a DESC NULLS FIRST]@2 as summation1]
---AggregateExec: mode=Single, gby=[d@2 as d, a@0 as a],
aggr=[SUM(annotated_data_infinite2.c)], ordering_mode=PartiallySorted([1])
-----StreamingTableExec: partition_sizes=1, projection=[a, c, d],
infinite_source=true, output_ordering=[a@0 ASC NULLS LAST]
-
-query III
+statement error DataFusion error: This feature is not implemented: ORDER BY is
not implemented for SUM
Review Comment:
I hadn't thought about the implications for `SUM(ORDER BY ...)` for floats 🤔
It appears that this is consistent with what postgres does:
```sql
postgres=# create table foo (x float);
CREATE TABLE
postgres=# insert into foo values (1.0);
INSERT 0 1
postgres=# insert into foo values (2.0);
INSERT 0 1
postgres=# insert into foo values (-1.0);
INSERT 0 1
postgres=# select sum(x ORDER BY x) from foo;
sum
-----
2
(1 row)
postgres=# select sum(x IGNORE NULLS) from foo;
ERROR: syntax error at or near "IGNORE"
LINE 1: select sum(x IGNORE NULLS) from foo;
^
postgres=#
```
I also verified that postgres actually does sort the input:
```sql
postgres=# explain select sum(x ORDER BY x) from foo;
QUERY PLAN
-------------------------------------------------------------------
Aggregate (cost=169.81..169.82 rows=1 width=8)
-> Sort (cost=158.51..164.16 rows=2260 width=8)
Sort Key: x
-> Seq Scan on foo (cost=0.00..32.60 rows=2260 width=8)
(4 rows)
postgres=#
```
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