'Provide a hook to override the generation of an
UPDATE..FROM clause.
MySQL and MSSQL override this.'

def update_from_clause(self, update_stmt, from_table, extra_froms, from_hints, **kw):

    return ('FROM    ' + ',    '.join((t._compiler_dispatch(self, asfrom=True, fromhints=from_hints, **kw) for t in extra_froms)))
