'Add special MySQL keywords in place of DISTINCT.
.. note::
this usage is deprecated.  :meth:`.Select.prefix_with`
should be used for special keywords at the start
of a SELECT.'

def get_select_precolumns(self, select):

    if isinstance(select._distinct, util.string_types):
        return (select._distinct.upper() + '    ')
    elif select._distinct:
        return 'DISTINCT    '
    else:
        return ''
