fix: duplicate output for HashJoinExec in CollectLeft mode (#9757)

* fix: duplicate output for HashJoinExec in CollectLeft mode

* address review comments

* test fix after merging main

Author: korowa

datafusion/core/src/physical_optimizer/join_selection.rs

@@ -305,11 +305,6 @@ impl PhysicalOptimizerRule for JoinSelection {
 /// `CollectLeft` mode is applicable. Otherwise, it will try to swap the join sides.
 /// When the `ignore_threshold` is false, this function will also check left
 /// and right sizes in bytes or rows.
-///
-/// For [`JoinType::Full`], it can not use `CollectLeft` mode and will return `None`.
-/// For [`JoinType::Left`] and [`JoinType::LeftAnti`], it can not run `CollectLeft`
-/// mode as is, but it can do so by changing the join type to [`JoinType::Right`]
-/// and [`JoinType::RightAnti`], respectively.
 fn try_collect_left(
     hash_join: &HashJoinExec,
     ignore_threshold: bool,
@@ -318,38 +313,20 @@ fn try_collect_left(
 ) -> Result<Option<Arc<dyn ExecutionPlan>>> {
     let left = hash_join.left();
     let right = hash_join.right();
-    let join_type = hash_join.join_type();
 
-    let left_can_collect = match join_type {
-        JoinType::Left | JoinType::Full | JoinType::LeftAnti => false,
-        JoinType::Inner
-        | JoinType::LeftSemi
-        | JoinType::Right
-        | JoinType::RightSemi
-        | JoinType::RightAnti => {
-            ignore_threshold
-                || supports_collect_by_thresholds(
-                    &**left,
-                    threshold_byte_size,
-                    threshold_num_rows,
-                )
-        }
-    };
-    let right_can_collect = match join_type {
-        JoinType::Right | JoinType::Full | JoinType::RightAnti => false,
-        JoinType::Inner
-        | JoinType::RightSemi
-        | JoinType::Left
-        | JoinType::LeftSemi
-        | JoinType::LeftAnti => {
-            ignore_threshold
-                || supports_collect_by_thresholds(
-                    &**right,
-                    threshold_byte_size,
-                    threshold_num_rows,
-                )
-        }
-    };
+    let left_can_collect = ignore_threshold
+        || supports_collect_by_thresholds(
+            &**left,
+            threshold_byte_size,
+            threshold_num_rows,
+        );
+    let right_can_collect = ignore_threshold
+        || supports_collect_by_thresholds(
+            &**right,
+            threshold_byte_size,
+            threshold_num_rows,
+        );
+
     match (left_can_collect, right_can_collect) {
         (true, true) => {
             if should_swap_join_order(&**left, &**right)?
@@ -916,9 +893,9 @@ mod tests_statistical {
     }
 
     #[tokio::test]
-    async fn test_left_join_with_swap() {
+    async fn test_left_join_no_swap() {
         let (big, small) = create_big_and_small();
-        // Left out join should alway swap when the mode is PartitionMode::CollectLeft, even left side is small and right side is large
+
         let join = Arc::new(
             HashJoinExec::try_new(
                 Arc::clone(&small),
@@ -942,32 +919,18 @@ mod tests_statistical {
             .optimize(join.clone(), &ConfigOptions::new())
             .unwrap();
 
-        let swapping_projection = optimized_join
-            .as_any()
-            .downcast_ref::<ProjectionExec>()
-            .expect("A proj is required to swap columns back to their original order");
-
-        assert_eq!(swapping_projection.expr().len(), 2);
-        let (col, name) = &swapping_projection.expr()[0];
-        assert_eq!(name, "small_col");
-        assert_col_expr(col, "small_col", 1);
-        let (col, name) = &swapping_projection.expr()[1];
-        assert_eq!(name, "big_col");
-        assert_col_expr(col, "big_col", 0);
-
-        let swapped_join = swapping_projection
-            .input()
+        let swapped_join = optimized_join
             .as_any()
             .downcast_ref::<HashJoinExec>()
             .expect("The type of the plan should not be changed");
 
         assert_eq!(
             swapped_join.left().statistics().unwrap().total_byte_size,
-            Precision::Inexact(2097152)
+            Precision::Inexact(8192)
         );
         assert_eq!(
             swapped_join.right().statistics().unwrap().total_byte_size,
-            Precision::Inexact(8192)
+            Precision::Inexact(2097152)
         );
         crosscheck_plans(join.clone()).unwrap();
     }