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https://issues.apache.org/jira/browse/CALCITE-5894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17753862#comment-17753862
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JingDas commented on CALCITE-5894:
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[~jhyde] I re-read this part of the paper again. I aggre with you, after “order
homogenization”, interesting order can be push down. If the interesting order
is above join, after push down,this give a chance to use `
EnumerableMergeJoin` instead of `EnumerableHashJoin` in the optimize because
one input of join is sorted. In another scene after “order homogenization” sort
maybe removed, which can not happen without “order homogenization”. I will log
a new Jira case for “order homogenization”.
> Add SortRemoveRedundantRule to remove redundant sort fields if they are
> functionally dependent on other sort fields
> -------------------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-5894
> URL: https://issues.apache.org/jira/browse/CALCITE-5894
> Project: Calcite
> Issue Type: New Feature
> Reporter: JingDas
> Assignee: JingDas
> Priority: Minor
> Labels: pull-request-available
>
> In some scene, Sort fields can be reduct, if sort fields contain unique key
> For example
> {code:java}
> SELECT ename, salary FROM Emp
> order by empno, ename{code}
> where `empno` is a key, `ename` is redundant since `empno` alone is
> sufficient to determine the order of any two records.
> So the SQL can be optimized as following:
> {code:java}
> SELECT name, Emp.salary FROM Emp
> order by empno{code}
> For another example:
> {code:java}
> SELECT e_agg.c, e_agg.ename
> FROM
> (SELECT count(*) as c, ename, job FROM Emp GROUP BY ename, job) AS e_agg
> ORDER BY e_agg.ename, e_agg.job, e_agg.c {code}
> Although `e_agg.ename` is not a key but field `ename` is unique and not null,
> it can be optimized as following:
> {code:java}
> SELECT e_agg.c, e_agg.ename
> FROM (SELECT count(*) as c, ename, job FROM Emp GROUP BY ename, job) AS e_agg
> ORDER BY e_agg.ename, e_agg.job{code}
> Sorting is an expensive operation, however. Therefore, it is imperative that
> sorting
> is optimized to avoid unnecessary sort field.
>
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