I don't think I've seen a HN post on user-defined variables. Why not? Are they bad to use? I can't find a lot about their best practices on the web. I'm curren

I don't think I've seen a HN post on user-defined variables. Why not? Are they bad to use? I can't find a lot about their best practices on the web. I'm currently learning SQL and being able to use variables would save a lot of time. I don't see the issue of not using them.