vlsi commented on a change in pull request #2329:
URL: https://github.com/apache/calcite/pull/2329#discussion_r562015869
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File path:
linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableDefaults.java
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@@ -4683,4 +4683,191 @@ private void flush() {
}
};
}
+
+ /**
+ * Merge Union Enumerable.
+ * Performs a union (or union all) of all its inputs (which must be already
sorted),
+ * respecting the order.
+ *
+ * @param sources input enumerables (must be already sorted)
+ * @param sortKeySelector sort key selector
+ * @param sortComparator sort comparator to decide the next item
+ * @param all whether duplicates will be considered or not
+ * @param equalityComparer {@link EqualityComparer} to control duplicates,
+ * only used if {@code all} is {@code false}
+ * @param <TSource> record type
+ * @param <TKey> sort key
+ */
+ public static <TSource, @Nullable TKey> Enumerable<TSource> mergeUnion(
Review comment:
The problem with `e1 == null ? null` is that behavior is not documented,
and it is not tested (there's no test which checks what happens in case
user-provided `keySelector` wants to convert `null` to something non-`null`).
`mergeUnion` method is already very generic (it has customization for
`keySelector`, `comparator`), so I see no reasons why the method should have
its own `null-handling`. It is generic enough to let users decide what they
want to do with nulls.
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