What ActiveRecord isn't is discoverable. Which is to an extent understandable. Its domain is literally anything you could express in SQL. But you really can do anything you want with it, you just have to find the right abstraction. A tool I use a lot is to .to_sql which will show you the compiled SQL fragment in a debugging session. You can compose with bare SQL fragments and ActiveRecord even includes an intermediate library so that you can work at the relational algebra level if you want.

It's not that ActiveRecord forces you to work a certain way. It just doesn't advertise all its features.

    Granted [SQL's] syntax is absolutely awful, but 
    it is a very useful and powerful language. The 
    concepts behind relational databases are embraced 
    by SQL in ways that I can't imagine in any other 
    language (I'm sure there must be other good relational 
    query languages somewhere, but I've never been exposed 
    to them)

It's somewhat significant, I think, that when Microsoft came up with LINQ (sort of a language- and backend- agnostic query language) they basically settled on something that looks like SQL but puts the FROM clause first, mainly so the editor can give you typing hints.

I'm not saying LINQ was a rousing success, but that was a pretty major greenfield MS devtools initiative and they have some pretty smart language/compiler people, so it's interesting that they settled on something not too different from good ol' SQL.