Fabian Hueske created FLINK-40915:
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Summary: Relax non-deterministic join-condition check for LATERAL
SNAPSHOT join
Key: FLINK-40915
URL: https://issues.apache.org/jira/browse/FLINK-40915
Project: Flink
Issue Type: Improvement
Components: Table SQL / Planner
Reporter: Fabian Hueske
In `StreamNonDeterministicUpdatePlanVisitor.visitJoin`, the generic join
handling rejects a non-deterministic join condition whenever the join output
may carry updates (build side updates) or for LEFT joins. The LATERAL SNAPSHOT
join (LSJ) currently goes through this generic check, but it is stricter than
necessary for LSJ: the LSJ output is append-only, and the join condition is
evaluated only once per probe row at join time. It is never re-evaluated when
build rows are retracted (build retractions match the operator's internal
whole-row-keyed multiset by row equality), so a non-deterministic condition
cannot cause the retraction-matching corruption the check guards against. As a
result, valid LSJ queries with a non-deterministic join condition (e.g. an
updating build side, or a LEFT LSJ even with insert-only inputs) are rejected
unnecessarily under TRY_RESOLVE.
Proposed change:
* exclude StreamPhysicalLateralSnapshotJoin from the
non-deterministic-condition check in visitJoin.
* Add tests covering a non-deterministic join condition with an updating build
side and a LEFT LSJ variant, and confirm regular-join behavior is unchanged
(NonDeterministicDagTest).
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