语句如下：

    1. update_stmt:
    2.     UPDATE table_factor
    3.        SET column_assign_list
    4.     [WHERE condition]
    5.     [ORDER BY order_expression_list]
    6.     [LIMIT limit_row_count];
    8. column_assign_list:
    9.     column_assign [, column_assign ...]
    11. column_assign:
    12.     column_name = expression
    14. condition:
    15.     expression
    17. order_expression_list:
    18.     order_expression [, order_expression ...]
    20. order_expression:
    21.     expression [ASC | DESC]
    23. limit_row_count:
    24.     INT_VALUE