hsyuan commented on a change in pull request #1995:
URL: https://github.com/apache/calcite/pull/1995#discussion_r436302600
##########
File path:
core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableNestedLoopJoin.java
##########
@@ -118,6 +124,64 @@ public static EnumerableNestedLoopJoin create(
return cost;
}
+ @Override public Pair<RelTraitSet, List<RelTraitSet>> passThroughTraits(
+ final RelTraitSet required) {
+ RelCollation collation = required.getCollation();
+ if (collation == null
+ || collation == RelCollations.EMPTY
+ || joinType == JoinRelType.FULL
+ || joinType == JoinRelType.RIGHT) {
+ return null;
+ }
+
+ // EnumerableNestedLoopJoin 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.
+
+
+ for (RelFieldCollation fc : collation.getFieldCollations()) {
+ // If field collation belongs to right input: cannot push down collation.
+ if (fc.getFieldIndex() >= getLeft().getRowType().getFieldCount()) {
+ return null;
+ }
+ }
+
+ RelTraitSet passthroughTraitSet = traitSet.replace(collation);
+ return Pair.of(passthroughTraitSet,
+ ImmutableList.of(
+ passthroughTraitSet,
+ passthroughTraitSet.replace(RelCollations.EMPTY)));
+ }
+
+ @Override public Pair<RelTraitSet, List<RelTraitSet>> deriveTraits(
+ final RelTraitSet childTraits, final int childId) {
+ // should only derive traits (limited to collation for now) from left join
input.
+ assert childId == 0;
+
+ RelCollation collation = childTraits.getCollation();
+ if (collation == null
+ || collation == RelCollations.EMPTY
+ || joinType == JoinRelType.FULL
+ || joinType == JoinRelType.RIGHT) {
+ return null;
+ }
+
+ return Pair.of(
+ getTraitSet().replace(collation),
+ ImmutableList.of(childTraits, right.getTraitSet()));
Review comment:
We also need to replace childTraits with enumerable convention. also
hashjoin.
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