def get_sql_update_numchild(self, path, incdec='inc'):
        """:returns: The sql needed the numchild value of a node"""
        sql = "UPDATE %s SET numchild=numchild%s1"\
              " WHERE path=%%s" % (
                  connection.ops.quote_name(
                      get_result_class(self.node_cls)._meta.db_table),
                  {'inc': '+', 'dec': '-'}[incdec])
        vals = [path]
        return sql, vals
:returns: The sql needed the numchild value of a node