With a normalized database schema, SQL optimization tends to focus on aspects outside the query, like making sure indexes get put in the currect locations. But I happen to be stuck with large and slightly-non-normalized tables. So, in order to write queries against these tables for a site that averages 30k hits per month, I need to be able to see what MySQL is doing with each query. For this I would be lost without EXPLAIN and SQL_NO_CACHE.

I don’t like writing tutorials, and I don’t really have time. But I love linking to great documentation. Most of what I know about MySQL I learned from their documentation, and I encourage even experienced query writers to make sure they know the importance of testing query times with SQL_NO_CACHE or using a development environment with caching completely disabled. When it comes to web applications, even microseconds can hurt in the long run.