select_to_base causes strange routes

https://github.com/blaze/odo/blob/master/odo/backends/sql.py#L441

If I have a select whose dshape is `int32` and do `odo(select([col]), str)` it will find the `select_to_base` edge for select -> str which will execute the select and return the result, even though the result is an `int`