PaulJackson123 commented on code in PR #3495:
URL: https://github.com/apache/calcite/pull/3495#discussion_r1379319973
##########
core/src/main/java/org/apache/calcite/rel/metadata/RelMdColumnUniqueness.java:
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@@ -266,21 +276,13 @@ public Boolean areColumnsUnique(Intersect rel,
RelMetadataQuery mq,
}
}
- // If no columns can affect uniqueness, then return unknown
- if (childColumns.cardinality() == 0) {
- return null;
- }
-
Review Comment:
An empty set can be unique. It is when all columns in the relation are
unique.
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