adriangb commented on code in PR #17201:
URL: https://github.com/apache/datafusion/pull/17201#discussion_r2280521294
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datafusion/sqllogictest/test_files/push_down_filter.slt:
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@@ -286,5 +286,37 @@ explain select a from t where CAST(a AS string) = '0123';
physical_plan DataSourceExec: file_groups={1 group:
[[WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/push_down_filter/t.parquet]]},
projection=[a], file_type=parquet, predicate=CAST(a@0 AS Utf8View) = 0123
+# Test dynamic filter pushdown with swapped join inputs (issue #17196)
+# Create tables with different sizes to force join input swapping
+statement ok
+copy (select i as k from generate_series(1, 100) t(i)) to
'test_files/scratch/push_down_filter/small_table.parquet';
+
+statement ok
+copy (select i as k, i as v from generate_series(1, 1000) t(i)) to
'test_files/scratch/push_down_filter/large_table.parquet';
+
+statement ok
+create external table small_table stored as parquet location
'test_files/scratch/push_down_filter/small_table.parquet';
+
+statement ok
+create external table large_table stored as parquet location
'test_files/scratch/push_down_filter/large_table.parquet';
+
+# Test that dynamic filter is applied to the correct table after join input
swapping
+# The small_table should be the build side, large_table should be the probe
side with dynamic filter
+query TT
+explain select * from small_table join large_table on small_table.k =
large_table.k where large_table.v >= 50;
+----
+physical_plan
+01)CoalesceBatchesExec: target_batch_size=8192
+02)--HashJoinExec: mode=CollectLeft, join_type=Inner, on=[(k@0, k@0)]
+03)----DataSourceExec: file_groups={1 group:
[[WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/push_down_filter/small_table.parquet]]},
projection=[k], file_type=parquet
+04)----RepartitionExec: partitioning=RoundRobinBatch(4), input_partitions=1
+05)------DataSourceExec: file_groups={1 group:
[[WORKSPACE_ROOT/datafusion/sqllogictest/test_files/scratch/push_down_filter/large_table.parquet]]},
projection=[k, v], file_type=parquet, predicate=v@1 >= 50 AND
DynamicFilterPhysicalExpr [ true ], pruning_predicate=v_null_count@1 !=
row_count@2 AND v_max@0 >= 50, required_guarantees=[]
Review Comment:
My understanding is that _at runtime_ (i.e. when `ExecutionPlan::execute` is
called and work actually begins) the left side is always the build side and the
right side is always the probe side. During optimizer passes which one is left
and right may be swapped / re-arranged but all of the dynamic filter stuff
happens after this so we can always push the filters into the right side. At
least for inner joins, other join types may be more complex and I haven't even
begun to wrap my head around those cases.
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