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https://issues.apache.org/jira/browse/CALCITE-6877?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17934043#comment-17934043
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Niels Pardon commented on CALCITE-6877:
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> Why were the tests added to RelToSqlConverterTest? They have nothing to do
> with SQL generation.
I couldn't find any existing tests for the RelRoot class specifically. We can
also move it into a new RelRootTest unit test class if you prefer that.
> Generate LogicalProject in RelRoot.project() when mapping is not name trivial
> -----------------------------------------------------------------------------
>
> Key: CALCITE-6877
> URL: https://issues.apache.org/jira/browse/CALCITE-6877
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.38.0
> Reporter: Niels Pardon
> Assignee: Niels Pardon
> Priority: Minor
> Labels: pull-request-available
> Fix For: 1.39.0
>
>
> Currently, the RelRoot.project() method only generates a project relation if
> the RelRoot fields are:
> * not ref trivial
> * or if one of the following is not true:
> ** is not a DML operation
> ** is not a force project
> ** the existing top relation is not already a LogicalProject
> [https://github.com/apache/calcite/blob/802fce3c41be76fca899ddb8c856d72c754d1520/core/src/main/java/org/apache/calcite/rel/RelRoot.java#L163-L169]
> The result is that for a simple SQL query that selects a single field from a
> table and renames the same field we are losing the renaming of the field if
> we call RelRoot.project() even if we set the force parameter to true since
> the relational tree embedded in the RelRoot already contains a LogicalProject
> at the top of the tree.
> My expectation would be that when I call RelRoot.project() that a
> LogicalProject is being added also if the RelRoot fields are not name trivial
> aka they are being renamed.
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