'append the given columns clause prefix expression to this select()
construct.
This is an **in-place** mutation method; the
:meth:`~.Select.prefix_with` method is preferred, as it provides standard
:term:`method chaining`.'

def append_prefix(self, clause):

    clause = _literal_as_text(clause)
    self._prefixes = (self._prefixes + (clause,))
