zzwqqq commented on code in PR #5385:
URL: https://github.com/apache/calcite/pull/5385#discussion_r4514596912
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core/src/main/java/org/apache/calcite/sql2rel/RelDecorrelator.java:
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@@ -464,9 +497,48 @@ public RelNode removeCorrelationViaRule(RelNode root) {
* {@link org.apache.calcite.rel.core.Correlate}s might be removable in such
way).
*/
public RelNode removeCorrelationViaRule(RelNode root, RuleSet ruleSet) {
+ root = prepareCorrelates(root);
return applyHepProgram(root, ruleSetToHepProgram(ruleSet));
}
+ /** Removes unused RHS computations before matching rules or building frames.
+ * The checked input must also be the input used by the rewrite.
+ */
+ private RelNode prepareCorrelates(RelNode root) {
+ final RelNode prepared = root.accept(new RelHomogeneousShuttle() {
+ @Override public RelNode visit(RelNode other) {
+ final RelNode rel = super.visit(other);
+ if (!(rel instanceof Correlate)) {
+ return rel;
+ }
+ final Correlate correlate = (Correlate) rel;
+ RelNode right = correlate.getRight();
+ if (!isDeterministic(right)) {
+ final RelBuilder trimBuilder =
relBuilderFactory().create(right.getCluster(), null);
+ final RelNode trimmed = new RelFieldTrimmer(null,
trimBuilder).trim(right);
Review Comment:
Sorry, my earlier explanation was incomplete: Using `RelFieldTrimmer.trim`
on the whole plan before decorrelation can remove a key that is unused by the
query but needed by the scalar uniqueness check. `trimPreservingBindings`
leaves the Correlate's left input unchanged, so that key is preserved.
However, applying `trimPreservingBindings` globally can remove the `Project`
below a `SINGLE_VALUE` aggregate, preventing the scalar rule from eliminating
that aggregate. I'd prefer to keep trimming local in this PR. Does that sound
good?
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