amaliujia commented on a change in pull request #2023:
URL: https://github.com/apache/calcite/pull/2023#discussion_r439609801
##########
File path:
core/src/main/java/org/apache/calcite/adapter/enumerable/EnumTraitsUtils.java
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@@ -148,4 +149,52 @@ private static boolean isCollationOnTrivialExpr(
return null;
}
}
+
+ // EnumerableNestedLoopJoin and EnumerableBatchNestedLoopJoin traits
passdown shall only
+ // pass through collation to left input. It is because for
EnumerableNestedLoopJoin always
+ // uses left input as the outer loop, thus only left input can preserve
ordering.
+ // Push sort both to left and right inputs does not help right outer join.
It's because in
+ // implementation, EnumerableNestedLoopJoin produces (null, right_unmatched)
all together,
+ // which does not preserve ordering from right side.
+ static Pair<RelTraitSet, List<RelTraitSet>>
passThroughTraitsForNestedLoopJoin(
Review comment:
Pushed a commit to make HashJoin and Correlate reuse the code. Also
rename this class to `EnumerableTraitUtils`
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