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https://issues.apache.org/jira/browse/CALCITE-3571?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16989312#comment-16989312
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Rui Wang commented on CALCITE-3571:
-----------------------------------
Could you give a higher level of description on the problem, what is the query,
what exception was given, etc. before dive into code analysis? Based on this
JIRA title looks like there is an exception thrown when there is a complex
expression in Join condition, when in which scenarios/query/case?
> RelBuilder#shouldMergeProject throws an exception for JOIN with complex
> conditions
> ----------------------------------------------------------------------------------
>
> Key: CALCITE-3571
> URL: https://issues.apache.org/jira/browse/CALCITE-3571
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.21.0
> Reporter: Kirill Kozlov
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Before joins are created left and right paths are pared first. For the 1st
> query above they are as follows:
> {code:java}
> Left:
> LogicalProject with RecordType(VARBINARY id, VARCHAR fA1, VARCHAR fA1_2)
> LogicalTableScan with RecordType(VARBINARY id, VARCHAR fA1)
> Right:
> LogicalTableScan with RecordType(VARCHAR id, VARCHAR fB1){code}
> As they are processed - they are registered as leaves (added to the Array).
>
> When Join node is being created it knows what the `condition expressions` is:
> {code:java}
> =(TO_HEX($0), $3)
> {code}
> Since TO_HEX is not computed anywhere - it modifies the left input to be as
> follows (via RelOptUtil#pushDownJoinConditions) because
> RelBuilder#shouldMergeProject always return true.
>
> {code:java}
> LogicalProject with RecordType(VARBINARY id, VARCHAR fA1, VARCHAR fA1_2,
> VARCHAR $f3)
> {code}
> where `VARCHAR $f3` is a result of TO_HEX. Note that the list of leaves is
> not updated.
> [https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java#L2571]
>
> Finally, when identifier "query.fA1_2" is being converted (via
> SqlToRelConverter#convertIdentifier) for the top-most node
> {code:java}
> top-most node:
> LogicalProject with RecordType(VARBINARY id, VARCHAR fA1, VARCHAR fA1_2,
> VARCHAR id0, VARCHAR fB1)
> LogicalJoin with RecordType(VARBINARY id, VARCHAR fA1, VARCHAR fA1_2,
> VARCHAR $f3, VARCHAR id0, VARCHAR fB1)
> LogicalProject with RecordType(VARBINARY id, VARCHAR fA1, VARCHAR fA1_2,
> VARCHAR $f3)
> LogicalTableScan with RecordType(VARBINARY id, VARCHAR fA1)
> LogicalTableScan with RecordType(VARCHAR id, VARCHAR fB1){code}
> Blackboard perform a lookup (via SqlToRelConverter#lookupExp), in process of
> which LookupContext is created.
> In a constructor, LookupContext performs flatten, which recursively traverses
> tree of nodes (from above codeblock) and checks the leaves to see if they
> contain such expression. When it does get to the modified left input of a
> join it does not get a match on it and continues further down to a TableScan.
> When it finally flattens the result, TableScan's RecordType knows nothing
> about a duplicated field `fA1_2`, causing an error above.
>
> I think a viable solution would be to modify Join creation to register a
> resulting join inputs as leaves (when they are modified). Alternative
> approach would be to not merge Projects when join needs to modify an input.
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