This seems like a lot of work to avoid implementing the best practice of encapsulating database logic in user-defined functions, views, and stored procedures rather than hard-coding queries.

With that (probably controversial) criticism aside, does this library support multiple conditions in a JOIN predicate?

Sorry to be so blunt, but this seems like something straight from TheDailyWTF. :/ Do you gain any abstraction over the underlying DBMS, like with using Doctrine?