Craig Kerstiens told me about this on our recent Postgres episode of The Changelog and my jaw about dropped out of my mouth.

… earlier today I was starting to wonder why couldn’t I do more machine learning directly inside [Postgres]. Yeah, there is madlib, but what if I wanted to write my own recommendation engine? So I set out on a total detour of a few hours and lo and behold, I can probably do a lot more of this in Postgres than I realized before. What follows is a quick walkthrough of getting a recommendation engine setup directly inside Postgres.

Craig doesn’t necessarily suggest you put this kind of solution in production, but he doesn’t come out and say don’t do it either. 😉