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https://issues.apache.org/jira/browse/CALCITE-2798?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16756842#comment-16756842
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Hongze Zhang commented on CALCITE-2798:
---------------------------------------
I am curious about what should happen if we remove the collations for all
logical rel nodes (except for LogicalSort).
Here is what ISO/IEC 9075-2 says:
{quote}The ordering of the rows of the table specified by the <query
expression> is guaranteed only for the that immediately contains the <order by
clause>
{quote}
I can see some optimizations will not be performed on logical rel nodes,
however it seems we can anyway apply them only for rel nodes that have physical
conventions.
And I feel that
[CALCITE-2593|https://issues.apache.org/jira/browse/CALCITE-2593] can also be
fixed by that.
> Optimizer should remove ORDER BY in sub-query, provided it has no LIMIT or
> OFFSET
> ---------------------------------------------------------------------------------
>
> Key: CALCITE-2798
> URL: https://issues.apache.org/jira/browse/CALCITE-2798
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.18.0
> Reporter: Vladimir Sitnikov
> Assignee: Julian Hyde
> Priority: Major
>
> The following SQL performs sort twice, however inner sort can be eliminated
> {code}select * from (
> select * from "emps"
> order by "emps"."deptno"
> ) order by 1 desc{code}
> The same goes for (window calculation will sort on its own)
> {code}select row_number() over (order by "emps"."deptno") from (
> select * from "emps"
> order by "emps"."deptno" desc
> ){code}
> The same goes for SetOp (union, minus):
> {code}select * from (
> select * from "emps"
> order by "emps"."deptno"
> ) union select * from (
> select * from "emps"
> order by "emps"."deptno" desc
> ){code}
> There might be other cases like that (e.g. Aggregate, Join, Exchange,
> SortExchange)
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