rubenada commented on code in PR #3311:
URL: https://github.com/apache/calcite/pull/3311#discussion_r1314830424
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linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableDefaults.java:
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@@ -4495,6 +4492,27 @@ private boolean advanceRight(TInner right, TKey
rightKey) {
}
}
+ public static int compareNullsLastForMergeJoin(@Nullable Comparable v0,
@Nullable Comparable v1) {
+ return compareNullsLastForMergeJoin(v0, v1, null);
+ }
+
+ public static int compareNullsLastForMergeJoin(@Nullable Comparable v0,
@Nullable Comparable v1,
+ @Nullable Comparator comparator) {
+ // Special code for mergeJoin algorithm: in case of two null values, they
must not be
+ // considered as equal (otherwise the join would return incorrect
results); instead, consider
+ // the first (left) value as "bigger", to advance on the right value and
continue with the
+ // algorithm
+ if (v0 == null && v1 == null) {
+ return 1;
Review Comment:
That is not correct, EnumerbleMergeJoin accepts inputs that are **already
sorted** (by some other operator on its left/right child, typically an
EnumerableSort, or some kind of InxedScan). So, the "first stage" that you
mention does not happen inside EnumerbleMergeJoin, which only performs your
"second stage". Therefore this "special comparator" (flagged as
"MergeJoinCompartor" in the auxiliary methods that generate it) will only be
used within EnumerbleMergeJoin code, and never outside of it.
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