如何創建更新觸發器

Question

我試圖創建項目時在訂單表都進入了產品表中的數量是假設減少

create or replace trigger quantity_dicr after update of quantity on products for each row 
declare 
    quantity float; 
    begin 
     select quantity into quantity from products where o_id = :new.o_id; 
     set quantity = quantity + :new.quantity , 
     where o_id= :new.o_id; 
    end quantity_dicr; 

表，將運行觸發器

create table products(
prod_id numeric not null, 
prod_name varchar2(50) not null, 
quantity numeric not null, 
price numeric not null, 
constraint prod_id_pk primary key(prod_id) 
) 
create table orders 
(
prod_id numeric not null, 
o_id numeric not null, 
quantity numeric not null, 
o_sum numeric not null, 
constraint fk_products foreign key (prod_id) references products(prod_id), 
constraint orders_pk primary key (o_id)) 
) 

它給了我這些錯誤

Error(4,64): PLS-00049: bad bind variable 'NEW.O_ID' 
Error(5,7): PL/SQL: SQL Statement ignored 
Error(5,11): PL/SQL: ORA-00922: missing or invalid option 
Error(6,19): PLS-00049: bad bind variable 'NEW.O_ID' 

任何可以遮光的幫助爲什麼有這些錯誤將有助於全

Answer 1

我想那一定是這一個：

create or replace trigger quantity_dicr 
    after update of quantity on orders 
    for each row 

觸發必須在訂單表，而不是表的產品進行定義。

順便說一句，如果新訂單（即插入訂單）會發生什麼情況。我認爲這也應該更新產品數量。

Answer 2

你的錯誤是在這裏

create or replace trigger quantity_dicr after update of quantity on products for each row 
declare 
    quantity float; 
begin 
    select quantity into quantity from products where o_id = :new.o_id; 
    set quantity = quantity + :new.quantity , 
    where o_id= :new.o_id; --Don't have field O_ID in table products 
end quantity_dicr; 

你可以做到這樣。

CREATE OR REPLACE TRIGGER quantity_dicr AFTER UPDATE ON orders FOR EACH ROW 
    UPDATE products SET quantity = quantity - :NEW.quantity WHERE prod_id = :NEW.prod_id; 
END quantity_dicr; 

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