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https://issues.apache.org/jira/browse/CALCITE-6009?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17766038#comment-17766038
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LakeShen commented on CALCITE-6009:
-----------------------------------
Thanks your advice,I've added a specific description.
> Add the optimize for removing the redundant Limit when a Limit's source row
> number less than Limit's fetch
> ----------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-6009
> URL: https://issues.apache.org/jira/browse/CALCITE-6009
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: LakeShen
> Priority: Major
>
> In calcite,Limit would be represented by Sort,such as `LogicalSort[fetch =
> 5]`.
> When the Limit' source row number is less than the Limit's fetch,we could
> remove the the redundant Limit.
> For example:
> {code:java}
> SELECT * FROM (VALUES 1,2,3,4,5,6) AS t1 LIMIT 10 {code}
> The plan tree is :
> {code:java}
> LogicalSort(fetch=[10])
> LogicalProject(t1=[$0])
> LogicalValues(tuples=[[{ 1 }, { 2 }, { 3 }, { 4 }, { 5 }, { 6 }]]) {code}
> Because the Limit's source max row number is 6,the Limit's fetch is 10,so we
> could remove the redundant Limit.
> Another example is :
> {code:java}
> SELECT count(*) FROM orders LIMIT 2 {code}
> The plan tree is :
> {code:java}
> LogicalSort(fetch=[2])
> LogicalAggregate(group=[{}], EXPR$0=[COUNT()])
> LogicalTableScan(table=[[tpch, ORDERS]]) {code}
> Because Limit's source max row number is 1,the Limit's fetch is 2, so we
> could remove the redundant Limit.
>
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