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https://issues.apache.org/jira/browse/CALCITE-6009?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17774237#comment-17774237
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Julian Hyde commented on CALCITE-6009:
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The way that this was combined with SORT_REMOVE_REDUNDANT (added in
CALCITE-5994) is confusing. That case removes Sort (when there is at most one
row); this case removes fetch (but only when there is no sort).
The documentation you added SORT_REMOVE_REDUNDANT doesn't explain the
situation. In CALCITE-6038 you need to improve the documentation significantly.
> Add optimization to remove redundant LIMIT that is more than input row count
> ----------------------------------------------------------------------------
>
> Key: CALCITE-6009
> URL: https://issues.apache.org/jira/browse/CALCITE-6009
> Project: Calcite
> Issue Type: New Feature
> Components: core
> Reporter: LakeShen
> Assignee: LakeShen
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.36.0
>
>
> 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.
> The logic is same as presto's RemoveRedundantLimit
> rule:https://github.com/prestodb/presto/blob/50fbc07111ecca60a1a5e62755f095fa204120d0/presto-main/src/main/java/com/facebook/presto/sql/planner/iterative/rule/RemoveRedundantLimit.java#L27
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