Worked on the datametica/calcite repository to enhance the correctness and reliability of SQL query processing, specifically addressing issues with the QUALIFY clause in final projections. Focused on Java and SQL, the developer identified and fixed a bug where fields used in the QUALIFY clause were omitted from the final output, which could lead to inaccurate analytics results. To ensure ongoing stability, regression tests were added to validate the new behavior and prevent future regressions. This work improved both the accuracy of query results and the maintainability of the codebase, with an emphasis on thorough testing and robust SQL logic.