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https://issues.apache.org/jira/browse/SPARK-59992?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gengliang Wang reassigned SPARK-59992:
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Assignee: Richard Chen
> element_at and array index are wrongly non-nullable under ANSI mode when the
> index is nullable
> ----------------------------------------------------------------------------------------------
>
> Key: SPARK-59992
> URL: https://issues.apache.org/jira/browse/SPARK-59992
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 4.2.0
> Reporter: Richard Chen
> Assignee: Richard Chen
> Priority: Major
> Labels: pull-request-available
>
> With ANSI mode enabled, ElementAt and GetArrayItem report nullable = false
> for a non-foldable index whenever the array is non-nullable and its elements
> are non-nullable (e.g. array('a', 'b')). The nullability of the index is
> ignored, even though both expressions are null-intolerant and return NULL for
> a NULL index.
> The optimizer trusts this flag. NullPropagation truncates a Coalesce after
> its first non-nullable child, so a fallback such as coalesce(element_at(arr,
> idx), 'z') is removed. The null then lands in a column the plan treats as
> non-nullable, so no null marker is written and readers see whatever is in the
> slot: the query silently returns a wrong element, or fails with
> INVALID_ARRAY_INDEX.
> Expected rows: (z, z) and (a, a). Actual on master: the optimized plan
> contains no coalesce, and the query fails with "[INVALID_ARRAY_INDEX] The
> index -1 is out of bounds". Selecting only the first column returns (b), (a):
> the NULL-index row silently gets 'b'.
> Repro, with spark.sql.ansi.enabled=true:
> {code:sql}
> SELECT coalesce(element_at(array('a', 'b'), CAST(nullif(id, 0) AS INT)), 'z')
> AS v1,
> coalesce(array('a', 'b')[CAST(nullif(id, 0) AS INT) - 1], 'z') AS v2
> FROM range(2);
> {code}
> Expected rows: (z, z) and (a, a). Actual: the optimized plan contains no
> coalesce (e.g. "if ((id = 0)) null else element_at([a,b], cast(id as int),
> None, true)"), the first row is (NULL, NULL), and the schema declares both
> columns non-nullable.
> The cause is GetArrayItemUtil.computeNullabilityFromArray, shared by both
> expressions:
> {code:scala}
> } else {
> if (failOnError) arrayElementNullable || child.nullable else true
> }
> {code}
> The fix is to also include ordinal.nullable in the ANSI branch; a
> non-nullable index keeps the existing non-nullable result.
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