Deepseek Coder is purpose-built for code-related tasks and excels at SQL query analysis, explaining execution plans, suggesting indexes, and rewriting inefficient queries. Paste your slow query along with your schema and it will walk through specific optimizations like avoiding full table scans, rewriting subqueries as joins, or adding covering indexes. Claude Sonnet is a strong alternative when you want detailed reasoning about trade-offs across different database engines. ChatGPT o-series edges ahead for complex multi-step query rewrites that benefit from its extended reasoning capability. GitHub Copilot is worth considering if you want inline suggestions directly inside your editor as you refactor the query.