如何在更新前后验证一行

Question

需要以某种方式编码，如果买家购买的数量超过库存控制台应该显示一条消息，即您现在只能购买可用数量，其余数量将很快更新，如果库存足够购买它应该显示请继续

简而言之，“在表 order_line 中插入一行之前验证现有数量并更新表库存的现有数量的函数、过程”

CREATE OR REPLACE PACKAGE order_package IS
          global_inv_id NUMBER (6);
          global_quantity NUMBER (6);
    PROCEDURE create_new_order(current_c_id NUMBER,
 current_meth_pmt VARCHAR2, current_os_id NUMBER);
   PROCEDURE create_new_order_line(current_o_id NUMBER);
       END;
        /


CREATE OR REPLACE PACKAGE BODY order_package IS

    PROCEDURE create_new_order(current_c_id NUMBER,
 current_meth_pmt VARCHAR2, current_os_id NUMBER) AS
         current_o_id NUMBER;
       BEGIN
         SELECT order_seq.NEXTVAL
         INTO  current_o_id
         FROM   dual;
           INSERT INTO orders
     VALUES(current_o_id, sysdate,current_meth_pmt, current_c_id,
       current_os_id);
          COMMIT;
       create_new_order_line(current_o_id);
       END create_new_order;
   PROCEDURE create_new_order_line(current_o_id NUMBER)AS
       BEGIN
       INSERT INTO order_line
    VALUES(current_o_id,global_inv_id, global_quantity);
         COMMIT;
        END create_new_order_line;
       END;
        /

Answer 1

您没有显示您的库存表，并且您的程序似乎没有数量订购值，因此其中一些是推测性的。您可能想要做的是首先更新该表并使用RETURNING INTO 子句获取更新后的库存。

UPDATE inventory SET global_quantity = global_quantity - order_quantity
 WHERE global_inv_id = current_c_id
RETURNING global_quantity INTO l_global_quantity;

IF l_global_quantity < 0 THEN
    ROLLBACK;
    raise_application_error( -20001, 'You ordered too much!' );
ELSE
    [... create order goes here ...]
END IF;

current_c_id 是正在订购的商品吗？这将引发一个异常，它应该被调用你的过程的任何东西捕获。如何向用户显示错误取决于所使用的应用程序层。