[Backport 2.19] Validate materialized view subqueries against SQL grammar deny list (#5485)

[RyanL1997]

Description

Validate materialized view subqueries against SQL grammar deny list

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

• Backport [Enhancement] Validate materialized view subqueries against SQL grammar deny list #5485

Check List

• New functionality includes testing.
• New functionality has been documented.
• New functionality has javadoc added.
• New functionality has a user manual doc added.
• New PPL command checklist all confirmed.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff or -s.
• Public documentation issue/PR created.

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PR Code Suggestions ✨

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Category	Suggestion	Impact
Possible issue	Add null check for indexQueryDetails Add null check for indexQueryDetails before accessing getMvQuery(). If SQLQueryUtils.extractIndexDetails() returns null, calling getMvQuery() will throw a NullPointerException. This could happen with malformed or unexpected query formats. async-query-core/src/main/java/org/opensearch/sql/spark/validator/SQLQueryValidator.java [49-55] public void validateFlintExtensionQuery(String sqlQuery, DataSourceType dataSourceType) { IndexQueryDetails indexQueryDetails = SQLQueryUtils.extractIndexDetails(sqlQuery); - String mvQuery = indexQueryDetails.getMvQuery(); - if (mvQuery != null) { - validate(mvQuery, dataSourceType); + if (indexQueryDetails != null) { + String mvQuery = indexQueryDetails.getMvQuery(); + if (mvQuery != null) { + validate(mvQuery, dataSourceType); + } } } Suggestion importance[1-10]: 7 __ Why: This is a valid defensive programming suggestion that prevents a potential NullPointerException if SQLQueryUtils.extractIndexDetails() returns null. While the suggestion addresses error handling, it's a moderate improvement since the actual behavior of extractIndexDetails() with malformed queries is unknown from the PR context.	Medium