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https://issues.apache.org/jira/browse/FLINK-39966?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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lincoln lee closed FLINK-39966.
-------------------------------
Resolution: Fixed
Fixed in master: e7084a6d634a33ec48e74a4bd1bc3c5f43759a03
> FlinkRelMdModifiedMonotonicity wrongly reports a non-time-attribute Top-1
> Rank as insert-only
> ---------------------------------------------------------------------------------------------
>
> Key: FLINK-39966
> URL: https://issues.apache.org/jira/browse/FLINK-39966
> Project: Flink
> Issue Type: Bug
> Components: Table SQL / Planner
> Affects Versions: 2.3.0, 2.2.1, 2.1.3
> Reporter: lincoln lee
> Assignee: lincoln lee
> Priority: Major
> Labels: pull-request-available
> Fix For: 2.4.0
>
>
> FLINK-34702 removed the dedicated StreamPhysicalDeduplicate handler from
> FlinkRelMdModifiedMonotonicity and re-routed deduplication monotonicity
> derivation through StreamPhysicalRank. The new dispatch guard is:
> case physicalRank: StreamPhysicalRank if RankUtil.isDeduplication(rel) =>
> RankUtil.isDeduplication only checks "Top-1 ROW_NUMBER without rank-number
> output". It is weaker than the condition the old StreamPhysicalDeduplicate
> node type implicitly guaranteed — that node only existed when
> RankUtil.canConvertToDeduplicate held, which additionally requires sorting on
> a single time attribute (sortOnTimeAttributeOnly).
> As a result, a Top-1 Rank whose ORDER BY is not a single time attribute (a
> regular column, or multiple columns) is mistakenly handled as an append-only
> FirstRow deduplication and reported as all-CONSTANT (insert-only) modified
> monotonicity. In reality such a Rank retracts and re-emits the kept row
> whenever a new winner arrives, so it produces updates.
> Downstream operators that consume this metadata then make wrong decisions —
> e.g. a MIN/MAX aggregation picks the non-retract variant instead of
> MIN_RETRACT/MAX_RETRACT, yielding incorrect query results.
>
> Reproduce:
> SELECT b, MIN(c) AS min_c
> FROM (
> SELECT a, b, c,
> ROW_NUMBER() OVER (PARTITION BY a ORDER BY b) AS rn -- ORDER BY a
> non-time column
> FROM MyTable
> ) WHERE rn = 1
> GROUP BY b
> The inner query is a Top-1 Rank that updates. The downstream MIN(c) is
> planned with the non-retract MIN (because the Rank output is treated as
> insert-only) instead of MIN_RETRACT, so retractions from the Rank are not
> handled and the aggregate result is wrong.
> Root cause: the dispatch guard dropped the sortOnTimeAttributeOnly invariant
> previously carried by the StreamPhysicalDeduplicate node type.
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