Simon Willison’s Weblog

4th March 2019 - Link Blog

MySQL: How to get the top N rows for each group. MySQL doesn’t support the row_number() window function that’s available in PostgreSQL (and recent SQLite), which means it can’t easily answer questions like “for each of these authors, give me the most recent three blog entries they have written” in a single query. Only it turns out it can, if you abuse MySQL session variables in a devious way. This isn’t a new feature: MySQL has had this for over a decade, and in my rough testing it works quickly even on tables with millions of rows.