If you want quality randomness you can always do some equivalent of ORDER BY RAND() as long as you get a new RAND() for each row. I've Googled around but didn'

If you want quality randomness you can always do some equivalent of ORDER BY RAND() as long as you get a new RAND() for each row. I've Googled around but didn't find anything about this trick: You can calculate a score and do something like ORDER BY RAND() * score to bias towards certain rows. This could be useful, e.g. you want to randomly show your most profitable items. The kNN method seems harder to generalize.