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https://issues.apache.org/jira/browse/CALCITE-4050?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17128722#comment-17128722
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Haisheng Yuan commented on CALCITE-4050:
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The 1-1 mapping is OK, the problem is that after map inversion, the mapping
becomes 0 to 0. But we first apply key 1, it can't find any target, we assume
it will break ordering, thus get empty collation.
The right child doesn't need to sorted by [1,0]. It can be [1], or [0], either
of which is OK.
> Traits Propagation for EnumerableMergeJoin Produces Incorrect Result
> --------------------------------------------------------------------
>
> Key: CALCITE-4050
> URL: https://issues.apache.org/jira/browse/CALCITE-4050
> Project: Calcite
> Issue Type: Bug
> Reporter: Jinpeng Wu
> Priority: Major
> Fix For: 1.24.0
>
>
> In EnumerableMergeJoin's deriveTraits method, it uses a Map to record mapping
> from left keys to right keys (the keyMap variable). However, the left keys
> could have duplicate entries.
> One example is JdbcTest.testJoinInCorrelatedSubQuery, the expected plan is
> EnumerableProject(deptno=[$0], name=[$1], employees=[$2], location=[$3])
> EnumerableMergeJoin(condition=[AND(=($0, $5), =($0, $4))], joinType=[inner])
> EnumerableSort(sort0=[$0], dir0=[ASC])
> EnumerableTableScan(table=[[hr, depts]])
> EnumerableSort(sort0=[$1], sort1=[$0], dir0=[ASC], dir1=[ASC])
> ...
> where left keys are [0, 0] , and right keys are [1, 0]. Deriving right
> child's traits may result in incorrect output.
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