How relational databases actually store, index, and count data — and how to reason about query performance from first principles.
When counting rows in a table, we reach for the count function out of habit. But the count function accepts several kinds of arguments, such as count(1), count(*), count(field), and so on. So which form of count delivers the best performance?
SELECT is usually the very first SQL statement anyone learns, yet few stop to ask what actually happens inside MySQL when that statement runs. This post walks through MySQL's server architecture and the full journey a SELECT query takes, from establishing the connection to the Executor handing the final result back to the client.
