amaliujia commented on a change in pull request #2005:
URL: https://github.com/apache/calcite/pull/2005#discussion_r436306942
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File path:
core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableCorrelate.java
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@@ -81,6 +87,35 @@ public static EnumerableCorrelate create(
traitSet, left, right, correlationId, requiredColumns, joinType);
}
+ @Override public Pair<RelTraitSet, List<RelTraitSet>> passThroughTraits(
+ final RelTraitSet required) {
+ final RelCollation collation = required.getCollation();
+ if (collation == null || collation == RelCollations.EMPTY) {
+ return null;
+ }
+
+ // EnumerableCorrelate traits passdown shall only pass through collation
to left input.
+ // This is because for EnumerableCorrelate always uses left input as the
outer loop,
+ // thus only left input can preserve ordering.
+
+ for (RelFieldCollation relFieldCollation : collation.getFieldCollations())
{
+ // If field collation belongs to right input: bail out.
+ if (relFieldCollation.getFieldIndex() >=
getLeft().getRowType().getFieldCount()) {
+ return null;
+ }
+ }
+
+ final RelTraitSet passThroughTraitSet = traitSet.replace(collation);
+ return Pair.of(passThroughTraitSet,
+ ImmutableList.of(
+ passThroughTraitSet,
+ passThroughTraitSet.replace(RelCollations.EMPTY)));
+ }
+
+ @Override public DeriveMode getDeriveMode() {
+ return DeriveMode.LEFT_FIRST;
+ }
Review comment:
Yes. Any collation can be derived from left input. Optimizer can decide
later if derived collations are useful.
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