amaliujia commented on a change in pull request #1995:
URL: https://github.com/apache/calcite/pull/1995#discussion_r435018987
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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) {
+ // Only consider exact key match for now
+ if (requiredKeySet.equals(leftKeySet)) {
+ return Pair.of(
+ required,
+ ImmutableList.of(
+ required,
+ required.replace(RelCollations.EMPTY)));
+ }
+ } else if (joinType == JoinRelType.RIGHT) {
+ // Only consider exact key match for now
+ if (requiredKeySet.equals(rightKeySet)) {
+ RelCollation rightCollation = RelCollations.shift(collation,
+ -left.getRowType().getFieldCount());
+ return Pair.of(
+ required,
+ ImmutableList.of(
+ required.replace(RelCollations.EMPTY),
+ required.replace(rightCollation)));
+ }
+ }
+
+ return null;
+ }
+
+// @Override public DeriveMode getDeriveMode() {
+// return DeriveMode.BOTH;
Review comment:
I confirmed that indeed EnumerableHashJoin always builds hash table on
right side.
For right/full outer join, to make result right, the implementation keeps a
set of keys from right side. During probing it also removes keys from that set.
At the end it will know how many keys from right side does not have a match
with left side, thus it can produces null with right tuples.
So I will prohibit traits propogation for right/full outer join.
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