如何在更新/插入之前创建一个异常，我必须将一个表的属性值与另一个表的属性值进行比较？

Posted 2023-03-28

【中文标题】如何在更新/插入之前创建一个异常，我必须将一个表的属性值与另一个表的属性值进行比较？

【英文标题】：How do I create an exception on before update/insert where I have to compare value of attribute of one table to the value of the attribute of another?

【发布时间】：2018-02-22 14:57:06

【问题描述】：

架构是

CUSTOMER(Cus_code, Cus_fname, Cus_lname, Cus_balance)

INVOICE(Inv_no, Cus_code, Inv_date, Inv_amount)

LINE(Inv_no, Line_no, P_code, Line_units, Line_price)

PRODUCT(P_code, P_desc, P_qoh, P_min, P_price, V_code)

VENDOR(V_code, V_name, V_Contact)

create or replace trigger inexcb
before update 
of invoice.Inv_amount,customer.cus_balance
on invoice,customer  
for each row
when (invoice.Inv_amount>customer.cus_balance)
where invoice.cus_balance=customer.cus_balance
declare
excep1 exception;
begin
raise excep1;
dbms_output.put_line='Invoice amount becoming more than Customer balance is 
not allowed.';
end;

【问题讨论】：

这甚至不会编译。 dbms_output.put_line 是一个过程调用，即

肯定'发票金额不能超过客户余额。'

对于自定义错误，请使用 raise_application_error(-20000,'Invoice amount .. blah blah blah');

现在关于您的“触发代码”......这个触发器应该在哪个表上？

【参考方案1】：

SQL> create or replace function inv_detail(inv_num char)
  2  return number is
  3  cus_bal number(6,2);
  4  begin
  5  select c.cus_balance into cus_bal from customer c
  6  where c.cus_code=inv_num;
  7  return cus_bal;
  8  end;
  9  /

Function created.

SQL> create or replace trigger thr_exce
  2  before insert on invoice
  3  for each row
  4  begin
  5  if :new.Inv_amount>inv_detail(:new.cus_code) then
  6  raise_application_error(-20200,'Invoice amount cannot be greater than customer balance');
  7  end if;
  8  end;
  9  /

Trigger created.

好吧，我只是用这个提交了我的作业，没有考虑引发真正的异常（由于时间的限制），但我猜就是这样。