Dandandan commented on code in PR #16716:
URL: https://github.com/apache/datafusion/pull/16716#discussion_r2194855680


##########
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:
   Thinking about this, I think a more generic version of this would be 
switching small left sides (e.g  < 10 rows) to using cross join :thinking: 



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