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https://issues.apache.org/jira/browse/CALCITE-5553?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17697172#comment-17697172
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Andrew Pilloud commented on CALCITE-5553:
-----------------------------------------
I think I have a workable fix now, which involves checking to ensure
`getType().isStruct()` is consistent for the fields before and after the
flatterer runs.
> Calcite RelStructuredTypeFlattener produces bad plan for single field structs
> -----------------------------------------------------------------------------
>
> Key: CALCITE-5553
> URL: https://issues.apache.org/jira/browse/CALCITE-5553
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.23.0, 1.28.0, 1.33.0
> Reporter: Andrew Pilloud
> Priority: Major
> Labels: pull-request-available
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> A Beam user brought us a query that produces an invalid plan after
> upgrading to a newer version of Beam (moving them from Calcite 1.20 to
> 1.28). I was able to write a test case which demonstrates this issue
> with a trivial filter on a table containing a nested struct with a
> single field. The issue appears to be coming out of
> RelStructuredTypeFlattener.rewrite and I bisected it to a single
> commit,
> [e44beba28|https://github.com/apache/calcite/commit/e44beba286ea9049c5fd00c3a3b0e4a4f1c03356].
> Removing the noFlatteningForInput function added in this commit fixes
> the issue. That method doesn't appear to be looking at types at all,
> only mismatches in field count, I expect so any single field struct
> would hit this. Any suggestions on how we can work around this in
> Beam?
> The test query and plans are as follows, the test case is in [PR
> 3092|https://github.com/apache/calcite/pull/3092].
> {code}
> select dn.skill from sales.dept_single dn WHERE dn.skill.type = ''
> {code}
> Expected plan:
> {noformat}
> LogicalProject(SKILL=[ROW($0)])
> LogicalFilter(condition=[=($0, '')])
> LogicalProject(TYPE=[$0.TYPE])
> LogicalTableScan(table=[[CATALOG, SALES, DEPT_SINGLE]])
> {noformat}
> Actual Plan:
> {noformat}
> LogicalProject(SKILL=[ROW($0)])
> LogicalFilter(condition=[=($0.TYPE, '')])
> LogicalProject(TYPE=[$0.TYPE])
> LogicalTableScan(table=[[CATALOG, SALES, DEPT_SINGLE]])
> {noformat}
> Plan before flatten:
> {noformat}
> LogicalProject(SKILL=[$0])
> LogicalFilter(condition=[=($0.TYPE, '')])
> LogicalTableScan(table=[[CATALOG, SALES, DEPT_SINGLE]])
> {noformat}
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