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https://issues.apache.org/jira/browse/FLINK-40794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18119200#comment-18119200
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Sergey Nuyanzin commented on FLINK-40794:
-----------------------------------------
Merged as
[c8fb3fb0973c9507489266a219d9af6c51cc177b|https://github.com/apache/flink/commit/c8fb3fb0973c9507489266a219d9af6c51cc177b]
> CAST in Table API ignores input nullability when the target type is NOT NULL
> ----------------------------------------------------------------------------
>
> Key: FLINK-40794
> URL: https://issues.apache.org/jira/browse/FLINK-40794
> Project: Flink
> Issue Type: Bug
> Components: Table SQL / Planner
> Reporter: Ramin Gharib
> Assignee: Ramin Gharib
> Priority: Major
> Labels: pull-request-available
>
> In the Table API, a CAST to a target written with .notNull() is planned as
> NOT NULL even when the input may be null. The CAST type strategy already
> derives the result as nullable, but CastConverter builds the RexNode from the
> literal target type. The optimizer trusts the wrong NOT NULL and can fold
> null checks away, which drops rows or produces wrong values.
> h3. Reproduce
> {code:java}
> Table t = tEnv.fromValues(
> ROW(FIELD("i", INT())),
> Row.of((Object) null),
> Row.of(1));
> t.select($("i").cast(BIGINT().notNull()).as("c"))
> .filter($("c").isNull())
> .execute()
> .print();
> {code}
> Expected: one row with c = NULL.
> Actual: empty result. The plan collapses to an empty Values because IS NULL
> is folded to FALSE.
> The same happens for a nested VARIANT input, e.g.
> parseJson(s).cast(ARRAY(VARIANT())).cast(ARRAY(INT()).notNull()). FLINK-40672
> only covered a top-level VARIANT input.
> SQL is not affected. A SQL CAST cannot declare NOT NULL on the target, and
> SqlCastFunction.deriveType takes the nullability from the input.
> h3. Proposed fix
> CastConverter should use the resolved output type of the call, which the type
> strategy derives from the input, instead of the literal target type. This
> aligns the Table API with SQL for all casts. As a side effect, casting a NOT
> NULL input to a nullable target now yields NOT NULL, as it already does in
> SQL.
> Also document on cast() that the top-level nullability of the target type is
> ignored.
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