[GitHub] [calcite] rubenada commented on a change in pull request #1995: [CALCITE-4012] Implement trait propagation for EnumerableHashJoin and…

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rubenada commented on a change in pull request #1995:
URL: https://github.com/apache/calcite/pull/1995#discussion_r433731666



##########
File path: core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableHashJoin.java
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@@ -100,6 +106,53 @@ public static EnumerableHashJoin create(
         condition, variablesSet, joinType);
   }
 
+  @Override public Pair<RelTraitSet, List<RelTraitSet>> passThroughTraits(
+      final RelTraitSet required) {
+    RelCollation collation = required.getCollation();
+    if (collation == null || collation == RelCollations.EMPTY) {
+      return null;
+    }
+
+    List<Integer> requiredKeys = RelCollations.ordinals(collation);
+    ImmutableBitSet requiredKeySet = ImmutableBitSet.of(requiredKeys);
+
+    ImmutableBitSet leftKeySet = ImmutableBitSet.of(joinInfo.leftKeys);
+    ImmutableBitSet rightKeySet = ImmutableBitSet.of(joinInfo.rightKeys)
+        .shift(left.getRowType().getFieldCount());
+
+    // HashJoin traits passdown shall only consider left/right outer join.
+    // It is because for a hash-based implementation, only non-hashed side can
+    // preserve ordering, thus only for left/right outer join, we are sure which
+    // side is non-hashed side (the outer child).
+    if (joinType == JoinRelType.LEFT) {

Review comment:
       Please note that currently EnumerableHashJoin implementation builds the hash table always on the right input.




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