PaulJackson123 commented on code in PR #3495:
URL: https://github.com/apache/calcite/pull/3495#discussion_r1408145985
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core/src/main/java/org/apache/calcite/rel/metadata/BuiltInMetadata.java:
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@@ -83,9 +83,9 @@ public interface UniqueKeys extends Metadata {
* represented as an {@link org.apache.calcite.util.ImmutableBitSet}, where
* each bit position represents a 0-based output column ordinal.
*
- * <p>Note that a key plus other columns is still unique. Therefore a table
- * with all columns unique has a unique key consisting of the empty set.
- * This is the case with all single-row tables.
+ * <p>Note that a unique key plus other columns is still unique.
+ * Conversely, all columns are unique in a table with a unique key
+ * consisting of the empty set, as is the case for all single-row tables.
Review Comment:
I changed the wording to accommodate the the zero-column case that you
mentioned - all zero-or-one-row tables have `()` as a key, but not all tables
that have all columns unique do.
However, I think it is true that all (even multi-row) tables with one or
more columns that have all columns unique have `()` as a unique key. So I might
be missing another point.
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