nuno-faria commented on code in PR #16716:
URL: https://github.com/apache/datafusion/pull/16716#discussion_r2194739991
##########
datafusion/physical-plan/src/joins/utils.rs:
##########
@@ -928,6 +929,55 @@ pub(crate) fn build_batch_from_indices(
Ok(RecordBatch::try_new(Arc::new(schema.clone()), columns)?)
}
+/// Returns a new [RecordBatch] resulting of a join where the build/left side
is empty.
+/// The resulting batch has [Schema] `schema`.
+pub(crate) fn build_batch_empty_build_side(
+ schema: &Schema,
+ build_batch: &RecordBatch,
+ probe_batch: &RecordBatch,
+ column_indices: &[ColumnIndex],
+ join_type: JoinType,
+) -> Result<RecordBatch> {
+ match join_type {
+ // these join types only return data if the left side is not empty, so
we return an
+ // empty RecordBatch
+ JoinType::Inner
Review Comment:
Cross joins with an empty relation already appear to run well in the
`CrossJoinExec` operator.
Here is the `CrossJoinExec` operator for `SELECT * FROM t1, t2`, where `t1`
has 100M rows and `t2` has none:
```
CrossJoinExec, metrics=[
output_rows=0,
elapsed_compute=351.714µs,
build_input_batches=0,
build_input_rows=0,
input_batches=0,
input_rows=0,
output_batches=0,
build_mem_used=0,
build_time=351.7µs,
join_time=12ns
]
```
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