SQL Oracle觸發器錯誤

Question

嗨，我想知道是否有人可以幫助我調整觸發器。 我僅與觸發器一起使用了僅幾周時間，這對我來說還是很新的。 我的觸發條件是，假設某條船遲交至customer_balance帳戶每天要增加$ 75。 如果該船提早歸還，則每天增加20美元，該船提早歸還到customer_Balance帳戶。 我一直在嘗試使此觸發器正常工作時出錯，因此我想知道是否可以幫助或向我解釋我做錯了什么。 謝謝。

create or replace trigger trig_penalty
        before update of customer_balance
    on customer  for each row
declare
   i number;
   s varchar(20);
begin
   select customer_balance into s
     from customer
    where customer_ID =:new.customer_id;

    i := :new.charter_returndate - :old.charter_duedate;
    if i>=0 then
       dbms_output.put_line('Late return fee added');
       update customer
          set customer_balance=customer_balance+75*i
        where customer_id=s;
    else 
       dbms_output.put_line('Early return refund added');
       update customer
          set customer_balance=customer_balance+20*i
        where customer_id=s;
    end if;
end;
/

Answer 1

好吧，您必須了解，觸發器是一種（在您的情況下）適用於被修改的每一行的工件。 因此，您正在對此進行不必要的工作。

嘗試這個：

create or replace trigger trig_penalty
        before update of customer_balance
    on customer  for each row
declare
   i number;
   s varchar(20);
begin
   --You dont need to select the id is it is already on :new.customer_id
   -- your trigger is for UPDATE
   ---select customer_balance into s
   ---  from customer
   --- where customer_ID := :new.customer_id;

    i := :new.charter_returndate - :old.charter_duedate;
    if i>=0 then
       --Do not use dbms_output in an internal object.
       --dbms_output.put_line('Late return fee added');

       --You don't need to run an update for an update trigger you
       -- just need to set the new value on :NEW.FIELD
       --update customer
       --   set customer_balance=customer_balance+75*i
       -- where customer_id=s;

       --As you select this value I'm using the OLD which means the value that 
       --Was already on the table

       :NEW.customer_balance := :OLD.customer_balance+75*i;

    else 
       --dbms_output.put_line('Early return refund added');
       --update customer
       --   set customer_balance=customer_balance+20*i
       -- where customer_id=s;

       :NEW.customer_balance := :OLD.customer_balance+20*i; 

    end if;
end;
/

那應該做。 請記住，在觸發之前，在：NEW上設置的值將最終顯示在表上。