Inside SQLite’s Frontend: How the Query Optimizer Makes Your SQL Fast

Hello, I'm Maneshwar. I'm building git-lrc, an AI code reviewer that runs on every commit. It is free, unlimited, and source-available on Github. Star Us to help devs discover the project. Do give it a try and share your feedback for improving the product. In the previous part, you saw how SQLite converts a parse tree into bytecode. At that point, SQLite knows exactly what to do and how to execute it. But there is still one critical question left. Is this the fastest way to do it? That is where the query optimizer comes in. It sits between parsing and code generation and decides how your query should actually be executed for the best performance. Why Optimization Exists at All Given a single SQL query, there are often multiple ways to execute it. Take a simple example: SELECT * FROM users WHERE age = 25; This query can be executed in different ways: Scan the entire table and check each row Use an index on age to directly find matching rows Both approaches produce the same result, but t