amaliujia commented on a change in pull request #2006:
URL: https://github.com/apache/calcite/pull/2006#discussion_r439783577
##########
File path:
core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMergeJoin.java
##########
@@ -134,31 +137,83 @@ public static boolean isMergeJoinSupported(JoinRelType
joinType) {
final RelTraitSet required) {
// Required collation keys can be subset or superset of merge join keys.
RelCollation collation = required.getCollation();
+ int leftInputFieldCount = left.getRowType().getFieldCount();
+
List<Integer> reqKeys = RelCollations.ordinals(collation);
- ImmutableBitSet reqKeySet = ImmutableBitSet.of(reqKeys);
+ List<Integer> leftKeys = joinInfo.leftKeys.toIntegerList();
+ List<Integer> rightKeys =
+ joinInfo.rightKeys.incr(leftInputFieldCount).toIntegerList();
+ List<Integer> rightKeysNotShifted = joinInfo.rightKeys.toIntegerList();
Review comment:
To this specific case, `toIntegerList` to get a list of key indexes (not
shifted, so index from 0). Then, later, in superset cases, we can use this list
to remove collations that are not on keys. Use this query as an example:
`select * from foo join bar on foo.a=bar.a and foo.b=bar.b order by bar.a,
bar.b, bar.c;
`
we can push
`collation a b to left`
`collation a, b, c to right`
Thus the output of join should still be sorted by a, b, c.
Then, the `toIntegerList` helps to to that only `a, b` needs to pushed to
left. It works along with
```
RelCollation rightCollation = RelCollations.shift(collation,
-leftInputFieldCount);
Mappings.TargetMapping mapping = buildMapping(false);
RelCollation leftCollation =
RexUtil.apply(
mapping,
removeCollationFieldsNotOnJoinKey(rightCollation,
rightKeysNotShifted));
```
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