JingsongLi commented on a change in pull request #9876: [FLINK-14134][table]
Introduce LimitableTableSource for optimizing limit
URL: https://github.com/apache/flink/pull/9876#discussion_r338967232
##########
File path:
flink-table/flink-table-planner-blink/src/test/resources/org/apache/flink/table/planner/plan/batch/sql/LimitTest.xml
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@@ -144,6 +186,27 @@ LogicalSort(fetch=[0])
<Resource name="planAfter">
<![CDATA[
Values(type=[RecordType(INTEGER a, BIGINT b, VARCHAR(2147483647) c)],
tuples=[[]], values=[a, b, c])
+]]>
+ </Resource>
+ </TestCase>
+ <TestCase name="testLimitWithLimitSource">
+ <Resource name="sql">
+ <![CDATA[SELECT a, c FROM LimitTable LIMIT 10]]>
+ </Resource>
+ <Resource name="planBefore">
+ <![CDATA[
+LogicalSort(fetch=[10])
++- LogicalProject(a=[$0], c=[$2])
+ +- LogicalTableScan(table=[[default_catalog, default_database, LimitTable]])
+]]>
+ </Resource>
+ <Resource name="planAfter">
+ <![CDATA[
+Calc(select=[a, c])
++- Limit(offset=[0], fetch=[10], global=[true])
+ +- Exchange(distribution=[single])
+ +- Limit(offset=[0], fetch=[10], global=[false])
Review comment:
And if we want to remove this local limit, we need check the child and check
whether it is a `LimitableTableSource` in `BatchExecLimitRule`. This
optimization is not worth the cost of coupling.
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