Relative paths are a must. I don't think I ever use non-relative paths.

Say you have a folder structure like this:

    sql/
      tables/
        foo.sql
        bar.sql
      main.sql

And the contents of main.sql are something like this:

      @@tables/foo.sql
      @@tables/foo.sql

Then you can run main.sql via: usql -f sql/main.sql

If script file resolution is not relative pathed to the parent, it gets very fragile as you must invoke the parent from a specific location, or, you have to hard code full pathes in your scripts (arguably even uglier).