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https://issues.apache.org/jira/browse/CALCITE-7680?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18101180#comment-18101180
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Yu Xu commented on CALCITE-7680:
--------------------------------
Thanks for the suggestions [~julianhyde] . I’d like to share my thoughts on the
currently implemented solution (please correct me if I’m mistaken): That's a
fair point for Sort-specific reasoning. However, the current implementation no
longer contains Sort-specific logic; it simply uses
{{{}RelMdUtil.isRelDefinitelyEmpty{}}}, which delegates the per-operator
reasoning to {{{}RelMdMaxRowCount{}}}. Keeping it in {{PruneEmptyRules}} avoids
duplicating the "replace with empty Values" logic and also covers other
definitely-empty cases like {{{}Filter(false){}}}. If we moved this to
{{{}SortRemoveRedundantRule{}}}, we would still need a separate mechanism for
non-Sort operators.
> PruneEmptyRules should prune Sort when OFFSET is greater than or equal to max
> input rows
> ----------------------------------------------------------------------------------------
>
> Key: CALCITE-7680
> URL: https://issues.apache.org/jira/browse/CALCITE-7680
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.42.0
> Reporter: Yu Xu
> Assignee: Yu Xu
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.43.0
>
>
> PruneEmptyRules currently misses the case where the Sort has an OFFSET that
> is large enough to skip every row the input can produce.
> eg：
> {code:java}
> @Test void testEmptySortOffsetGreaterThanMaxRows() {
> // The input VALUES has at most 2 rows, so 'OFFSET 5' skips them all.
> final String sql = "select * from (values (1, 2), (3, 4)) as t (a, b)\n"
> + "order by a\n"
> + "offset 5 rows";
> sql(sql).check();
> } {code}
> plan is：
> {code:java}
> LogicalSort(sort0=[$0], dir0=[ASC], offset=[5])
> LogicalProject(A=[$0], B=[$1])
> LogicalValues(tuples=[[{ 1, 2 }, { 3, 4 }]]) {code}
> We could actually improve PruneEmptyRules to make the plan to：
> {code:java}
> LogicalValues(tuples=[[]]){code}
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