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https://issues.apache.org/jira/browse/CALCITE-793?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14641133#comment-14641133
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Julian Hyde commented on CALCITE-793:
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I've seen changes from SUM to and from $SUM0 before. I agree, it seems to be
due to an unstable cost model. If your change fixes that instability that would
be great (it might cause a few test failures) -- go ahead and submit.
> The compiler asks for unnecessary collation trait on plan with materialized
> view
> --------------------------------------------------------------------------------
>
> Key: CALCITE-793
> URL: https://issues.apache.org/jira/browse/CALCITE-793
> Project: Calcite
> Issue Type: Bug
> Affects Versions: 1.4.0-incubating
> Reporter: Maryann Xue
> Assignee: Julian Hyde
> Fix For: next
>
> Attachments: CALCITE-793.patch
>
> Original Estimate: 120h
> Remaining Estimate: 120h
>
> When a query does not have an ORDER BY clause, we should ignore the collation
> trait of the main table plan and should not request the materialized view
> plan to have the same collation.
> For example, we have a table 'A' sorted by primary key 'id', and we have a
> materialized view 'V' projected from 'A' which is sorted by column 'col1'.
> And now we have a query like "select id, col0, col1, col2 from A where col1 <
> '10'".
> The main table plan will come out like a Filter on top of a TableScan of 'A',
> while the materialized view plan should also be something like a Filter on
> top of a TableScan of 'V' and it should not have a Sort, so that if doing a
> col1 related filter on col1 ordered table 'V' is cheaper, the materialized
> view plan will be chosen.
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