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https://issues.apache.org/jira/browse/CALCITE-62?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15035451#comment-15035451
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Julian Hyde commented on CALCITE-62:
------------------------------------
I have created a branch
https://github.com/julianhyde/calcite/tree/62-join-output-mapping with a
work-in-progress of one possible solution to this problem: adding a mapping
field to Join.
> Allow a RelNode in a RelSet to return columns in permuted order
> ---------------------------------------------------------------
>
> Key: CALCITE-62
> URL: https://issues.apache.org/jira/browse/CALCITE-62
> Project: Calcite
> Issue Type: Bug
> Reporter: GitHub Import
> Labels: github-import
>
> Currently a long planning process (e.g. JdbcTest.testIn) seems to fire a lot
> of rules about merging projects with projects, projects with calcs. I suspect
> that there are a lot of sets that are equivalent but for a permutation of the
> order of the columns.
> If each RelNode that was a member of a RelSet specified a permutation
> (possibly the identity) of its columns to match the order in the set, then
> many sets would be merged, and the search space would be much smaller.
> ProjectRels and CalcRels that are just a permutation (not to mention renames
> and the identity) would be identified and removed when the rel is registered.
> This change would increase complexity for people implementing rules. In
> addition to "RelNode RelOptRuleCall.rel(int)", there would be "Permutation
> RelOptRuleCall.permutation(int)", and we need to make sure that people
> remember to call permutation.
> Today people have to remember to write variants of a rule that match rels
> with and without intervening projects. With this change, the intervening
> projects would be rarer, so the simple rules would be applicable in more
> cases.
> ---------------- Imported from GitHub ----------------
> Url: https://github.com/julianhyde/optiq/issues/62
> Created by: [julianhyde|https://github.com/julianhyde]
> Labels: for-next-release,
> Created at: Thu Oct 17 18:39:02 CEST 2013
> State: open
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