simonvandel opened a new issue, #13483:
URL: https://github.com/apache/datafusion/issues/13483
### Describe the bug
In the following query
```sql
EXPLAIN SELECT
CASE
WHEN name = 'name1' THEN 0.0
WHEN name = 'name2' THEN 0.5
END AS a
FROM (
SELECT 'name1' AS name
UNION ALL
SELECT 'name2'
)
ORDER BY a DESC;
```
the order of a is not matching the `ORDER BY a DESC`.
The resulting plan looks like this:
```
+---------------+-------------------------------------------------------------------------------------------------------------------+
| plan_type | plan
|
+---------------+-------------------------------------------------------------------------------------------------------------------+
| logical_plan | Sort: a DESC NULLS FIRST
|
| | Projection: CASE WHEN name = Utf8("name1") THEN
Float64(0) WHEN name = Utf8("name2") THEN Float64(0.5) END AS a |
| | Union
|
| | Projection: Utf8("name1") AS name
|
| | EmptyRelation
|
| | Projection: Utf8("name2") AS name
|
| | EmptyRelation
|
| physical_plan | CoalescePartitionsExec
|
| | ProjectionExec: expr=[CASE WHEN name@0 = name1 THEN 0
WHEN name@0 = name2 THEN 0.5 END as a] |
| | UnionExec
|
| | ProjectionExec: expr=[name1 as name]
|
| | PlaceholderRowExec
|
| | ProjectionExec: expr=[name2 as name]
|
| | PlaceholderRowExec
|
| |
|
+---------------+-------------------------------------------------------------------------------------------------------------------+
```
As can be seen the `Sort` from the logical plan gets transformed into a
`CoalescePartitionsExec` in the physical plan.
However, the docs for `CoalescePartitionsExec`
https://docs.rs/datafusion/latest/datafusion/physical_plan/coalesce_partitions/struct.CoalescePartitionsExec.html
says that "No guarantees are made about the order of the resulting partition."
### To Reproduce
In datafusion-cli v 43:
```sql
EXPLAIN SELECT
CASE
WHEN name = 'name1' THEN 0.0
WHEN name = 'name2' THEN 0.5
END AS a
FROM (
SELECT 'name1' AS name
UNION ALL
SELECT 'name2'
)
ORDER BY a DESC;
```
### Expected behavior
Resulting order is consistent
### Additional context
Running
```sql
EXPLAIN VERBOSE SELECT
CASE
WHEN name = 'name1' THEN 0.0
WHEN name = 'name2' THEN 0.5
END AS a
FROM (
SELECT 'name1' AS name
UNION ALL
SELECT 'name2'
)
ORDER BY a DESC;
```
shows that the `EnforceSorting` pass seems to remove the SortExec
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