[CALCITE-7550] SqlUpdate and SqlDelete unparse EXISTS subqueries without parentheses

[zzwqqq]

Jira Link

CALCITE-7550

Changes Proposed

Fixes unparsing of EXISTS subqueries in UPDATE and DELETE statements.

SqlUpdate and SqlDelete were unparsing the WHERE condition directly, which could produce invalid SQL such as WHERE EXISTS SELECT ....

This change moves the existing WHERE unparsing logic from SqlSelectOperator into SqlUtil.unparseWhereClause and reuses it for SELECT, UPDATE, and DELETE, so DML statements use the same WHERE_LIST frame behavior as queries.

Adds regression tests for UPDATE and DELETE with EXISTS predicates.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
97.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[dssysolyatin]

Is the same problem valid for MERGE ? I think it is possible to specify EXISTS inside ON clause