xuzifu666 commented on code in PR #5040:
URL: https://github.com/apache/calcite/pull/5040#discussion_r3471600232
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core/src/main/java/org/apache/calcite/rel/metadata/RelMdCollation.java:
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@@ -372,13 +373,16 @@ public static List<RelCollation> sort(RelCollation
collation) {
/** Helper method to determine a
* {@link org.apache.calcite.rel.core.Window}'s collation.
*
- * <p>A Window projects the fields of its input first, followed by the output
- * from each of its windows. Assuming (quite reasonably) that the
- * implementation does not re-order its input rows, then any collations of
its
- * input are preserved. */
+ * <p>A Window operator groups rows by PARTITION BY keys and sorts each
+ * partition by ORDER BY keys. The output order is therefore not defined by
+ * a simple collation in the general case, so we conservatively report no
+ * collations. */
public static @Nullable List<RelCollation> window(RelMetadataQuery mq,
RelNode input,
ImmutableList<Window.Group> groups) {
- return mq.collations(input);
+ Util.discard(mq);
+ Util.discard(input);
+ Util.discard(groups);
+ return Collections.emptyList();
Review Comment:
Done, before this just to handle with unused warning.
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