libenchao commented on code in PR #3311:
URL: https://github.com/apache/calcite/pull/3311#discussion_r1314935681
##########
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:
Thanks for the explanation, it sounds good to me. Maybe my impression is
from that I searched the usage of this comparator, and found it's used here:
https://github.com/apache/calcite/blob/cbf857e319a695fe96b1f3f5f38a779821c92cb3/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableDefaults.java#L4393-L4401,
and here:
https://github.com/apache/calcite/blob/cbf857e319a695fe96b1f3f5f38a779821c92cb3/linq4j/src/main/java/org/apache/calcite/linq4j/EnumerableDefaults.java#L4426-L4434
I guess you are more familiar than me with this part, if these two places
are safe regarding this change, then I have no more concerns.
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