Worked on enhancing SQL query capabilities in the doctrine/dbal repository by implementing support for union main parts within Common Table Expressions (CTEs) using PHP and SQL. Developed features that allow the QueryBuilder to construct queries with WITH cte ... UNION ... syntax, enabling more expressive and flexible SQL generation for complex analytical use cases. Integrated these changes into the WithSQLBuilder and QueryBuilder components, focusing on maintainability and reducing reliance on raw SQL. Added comprehensive tests to validate union-CTE queries and ensure cross-database compatibility. The work emphasized robust database management practices and improved the clarity of the builder APIs for future development.