Worked on enhancing the stability and correctness of the PRQL/prql SQL backend by addressing two critical bugs affecting SQL generation for complex queries. Focused on compiler development and integration testing using Rust and SQL, the work involved fixing issues related to redundant CTEs with sorting and the correct translation of repeated and derived columns in SELECT and DERIVE statements. Each fix was accompanied by comprehensive regression tests, expanding the test suite to better cover CTE handling and column translation. These improvements reduced the risk of subtle regressions and increased the reliability and maintainability of the SQL backend for future development.