morrySnow commented on code in PR #67796:
URL: https://github.com/apache/doris/pull/67796#discussion_r4011634139
##########
fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/PushDownTopNDistinctThroughJoin.java:
##########
@@ -197,6 +201,34 @@ private List<OrderKey> getPushedOrderKeys(Set<Slot>
groupBySlots, Set<Slot> join
notFound = true;
}
}
- return pushedOrderKeys.build();
+ List<OrderKey> pushedOrderKeyList = pushedOrderKeys.build();
+ if (pushedOrderKeyList.size() == orderKeys.size()
+ || isOrderKeyPrefixUniqueAfterDistinct(joinChild,
pushedOrderKeyList)) {
+ return pushedOrderKeyList;
+ }
+ return ImmutableList.of();
+ }
+
+ /**
+ * A partial order-key prefix is safe for a hard limit only when it
uniquely orders the rows produced by
+ * {@link PlanUtils#distinct(Plan)}. This is true when a leading part of
the prefix either is already a
+ * non-null unique key, covers every child output, or functionally
determines every remaining child output.
+ */
+ private boolean isOrderKeyPrefixUniqueAfterDistinct(Plan joinChild,
List<OrderKey> orderKeyPrefix) {
+ Set<Slot> childOutput = joinChild.getOutputSet();
+ DataTrait childTrait = joinChild.getLogicalProperties().getTrait();
+ FuncDeps validFuncDeps = childTrait.getAllValidFuncDeps(childOutput);
Review Comment:
Fixed in 1866bef17b7. Empty prefixes now return before touching child
outputs/traits, full child-output coverage returns before trait lookup, and
non-null uniqueness short-circuits before any FD work. The remaining proof uses
a slot-indexed closure work queue over direct FD graph edges, so it no longer
materializes the full transitive relation or rescans it once per prefix slot;
graph expansion is O(V + E). Added closure coverage for transitive and compound
determinants. The targeted FE run passed PushDownTopNDistinctThroughJoinTest,
FuncDepsDGTest, and FdTest (27 tests, 0 failures/errors/skips).
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