Zhen Chen created CALCITE-7463:
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Summary: UnionToFilterRule incorrectly rewrites UNION with LIMIT
Key: CALCITE-7463
URL: https://issues.apache.org/jira/browse/CALCITE-7463
Project: Calcite
Issue Type: Bug
Components: core
Affects Versions: 1.41.0
Reporter: Zhen Chen
Fix For: 1.42.0
The {{UnionToFilterRule}} produces incorrect results when applied to inputs
that contain {{{}LIMIT{}}}.
Specifically, the rule incorrectly collapses:
{code:java}
(SELECT mgr, comm FROM emp LIMIT 2)
UNION
(SELECT mgr, comm FROM emp LIMIT 2){code}
into:
{code:java}
SELECT DISTINCT mgr, comm FROM emp LIMIT 2
{code}
This transformation is {*}not semantically equivalent{*}.
*Reproduction*
SQL
{code:java}
(SELECT mgr, comm FROM emp LIMIT 2)
UNION
(SELECT mgr, comm FROM emp LIMIT 2) {code}
h4. Plan Before
{code:java}
LogicalUnion(all=[false])
LogicalSort(fetch=[2])
LogicalProject(MGR=[$3], COMM=[$6])
LogicalTableScan(table=[[CATALOG, SALES, EMP]])
LogicalSort(fetch=[2])
LogicalProject(MGR=[$3], COMM=[$6])
LogicalTableScan(table=[[CATALOG, SALES, EMP]]) {code}
Plan After (Incorrect)
{code:java}
LogicalAggregate(group=[{0, 1}])
LogicalSort(fetch=[2])
LogicalProject(MGR=[$3], COMM=[$6])
LogicalTableScan(table=[[CATALOG, SALES, EMP]]) {code}
*Expected Behavior*
The transformation should NOT be applied when any input of UNION contains
LogicalSort(That contains ORDER BY, LIMIT, OFFSET).
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