Fabian Hueske created FLINK-40902:
-------------------------------------
Summary: LATERAL SNAPSHOT join wrongly rejected when a local
filter targets the join key column
Key: FLINK-40902
URL: https://issues.apache.org/jira/browse/FLINK-40902
Project: Flink
Issue Type: Bug
Components: Table SQL / Planner
Reporter: Fabian Hueske
A LATERAL SNAPSHOT join that has a valid equi-join predicate is wrongly
rejected with
"LATERAL SNAPSHOT join requires at least one equality predicate."
whenever the query also has a local filter on the same column that carries the
equi-join predicate.
Example (fails):
SELECT o.order_id, c.city
FROM orders AS o
JOIN LATERAL SNAPSHOT(
input => TABLE customers,
on_time => DESCRIPTOR(rowtime)
) AS c
ON o.customer_id = c.customer_id
WHERE o.customer_id = 3200;
A filter on any other (non-join-key) column, e.g. WHERE o.amount = 42, works
fine.
Root cause:
LogicalJoinToLateralSnapshotJoinRule enforces the equi-key requirement via
join.analyzeCondition().leftKeys.isEmpty(). When the local filter targets the
join key, Calcite's constant propagation pushes o.customer_id = 3200 to the
probe
side, infers customers.customer_id = 3200 on the build side, and then simplifies
the join condition o.customer_id = c.customer_id to TRUE. analyzeCondition()
then
reports no equi-keys and the rule rejects a join that is in fact an equi-join.
The
error message is also misleading, since an equality predicate was provided.
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