UBarney commented on code in PR #16443:
URL: https://github.com/apache/datafusion/pull/16443#discussion_r2202340283
##########
datafusion/physical-plan/src/joins/nested_loop_join.rs:
##########
@@ -828,13 +833,127 @@ impl<T: BatchTransformer> NestedLoopJoinStream<T> {
handle_state!(self.process_probe_batch())
}
NestedLoopJoinStreamState::ExhaustedProbeSide => {
- handle_state!(self.process_unmatched_build_batch())
+ handle_state!(self.prepare_unmatched_output_indices())
+ }
+ NestedLoopJoinStreamState::OutputUnmatchedBuildRows(_) => {
+ handle_state!(self.build_unmatched_output())
}
NestedLoopJoinStreamState::Completed => Poll::Ready(None),
};
}
}
+ fn get_next_join_result(&mut self) -> Result<Option<RecordBatch>> {
+ let (left_indices, right_indices, start) =
+ self.join_result_status.as_mut().ok_or_else(|| {
+ datafusion_common::_internal_datafusion_err!(
+ "should have join_result_status"
+ )
+ })?;
+
+ let left_batch = self
+ .left_data
+ .as_ref()
+ .ok_or_else(|| {
+ datafusion_common::_internal_datafusion_err!("should have
left_batch")
+ })?
+ .batch();
+
+ let right_batch = match &self.state {
+ NestedLoopJoinStreamState::ProcessProbeBatch(record_batch) =>
record_batch,
+ NestedLoopJoinStreamState::OutputUnmatchedBuildRows(record_batch)
=> {
+ record_batch
+ }
+ _ => {
+ return internal_err!(
+ "state should be ProcessProbeBatch or OutputUnmatchBatch"
+ )
+ }
+ };
+
+ let current_start = *start;
+
+ if left_indices.is_empty() && right_indices.is_empty() &&
current_start == 0 {
Review Comment:
> That was my initial approach. However, it resulted in an output with 0
rows and 0 columns, which seems to be incorrect and caused the test to fail.
You can see the failed CI run here:
https://github.com/apache/datafusion/actions/runs/15734253347/job/44343070926?pr=16443#step:5:1208
Now I understand why [this
test](https://github.com/apache/datafusion/blob/acf0bbe1cedf3fe0155de5f41a5b66046e262e04/datafusion/core/src/dataframe/mod.rs#L1250-L1263)
passed after I changed the return value from `None` to
`RecordBatch::new_empty`.
In this unit test, the join result is converted to a string and then
compared with the expected output. When converting to a string, it retrieves
the schema from the `record_batch` (as the passed `schema_opt` is `None`).
https://github.com/apache/arrow-rs/blob/7b219f98c25fcd318a0c207f51a41398d1b23724/arrow-cast/src/pretty.rs#L183-L187
When executed in the CLI, there's no issue even if the Nested Loop Join
(NLJ) returns 0 record batches.
```
> select t1.value from range(1) t1 join range(1) t2 on t1.value + t2.value
>100;
+-------+
| value |
+-------+
+-------+
0 row(s) fetched.
```
From a compatibility standpoint, I think it's better to keep it consistent
with the previous behavior.
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