[feature](Nereids): Pushdown TopN-Distinct through Union#27628
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starocean999
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keanji-x
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XuJianxu
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Dec 14, 2023
```
TopN-Distinct
-> Union All
-> child plan1
-> child plan2
-> child plan3
rewritten to
TopN-Distinct
-> Union All
-> TopN-Distinct
-> child plan1
-> TopN-Distinct
-> child plan2
-> TopN-Distinct
-> child plan3
```
morrySnow
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Jun 26, 2026
Issue Number: close #xxx Related PR: apache#27628 Problem Summary: PushDownTopNDistinctThroughUnion used the rewritten child plan output to map UNION output slots when pushing TopN distinct into UNION branches. For UNION DISTINCT queries with duplicate projection columns and window output, the child plan output can be shorter than the UNION regular child output, causing IndexOutOfBoundsException during rewrite. Use the UNION regular child output for slot remapping and add focused FE and regression coverage for duplicate output with window plus outer ORDER BY LIMIT. None - Test: Regression test / Unit Test - ./run-fe-ut.sh --run org.apache.doris.nereids.rules.rewrite.PushDownTopNDistinctThroughUnionTest - ./run-regression-test.sh --run -d nereids_rules_p0/push_down_top_n -s push_down_top_n_distinct_through_union -forceGenOut - Behavior changed: No - Does this need documentation: No
morrySnow
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Jun 26, 2026
Issue Number: close #xxx Related PR: apache#27628 Problem Summary: PushDownTopNDistinctThroughUnion used the rewritten child plan output to map UNION output slots when pushing TopN distinct into UNION branches. For UNION DISTINCT queries with duplicate projection columns and window output, the child plan output can be shorter than the UNION regular child output, causing IndexOutOfBoundsException during rewrite. Use the UNION regular child output for slot remapping and add focused FE and regression coverage for duplicate output with window plus outer ORDER BY LIMIT. None - Test: Regression test / Unit Test - ./run-fe-ut.sh --run org.apache.doris.nereids.rules.rewrite.PushDownTopNDistinctThroughUnionTest - ./run-regression-test.sh --run -d nereids_rules_p0/push_down_top_n -s push_down_top_n_distinct_through_union -forceGenOut - Behavior changed: No - Does this need documentation: No
This was referenced Jun 26, 2026
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