I've been using relational databases for 15 years and I've never "seen joins go bad". I don't even know what that means. I know some people avoid joins, but f

I've been using relational databases for 15 years and I've never "seen joins go bad". I don't even know what that means. I know some people avoid joins, but from my interactions with those people it has always been because they heard the myth that joins are slow, and foolishly figure writing a naive join implementation in PHP will be faster.