ORACLE中触发器在插入A表后自动修改B表数据么?

Question

  create or replace trigger sales_products
 after insert on sales
 begin
     update products set products.quantity=products.quantity-sales.quantity
     where sales.pid=products.pid;
 end;
这条语句应该如何修改?使得当有数据插入sales表的时候,自动修改products表中的quantity值SQL> desc sales
 名称                                      是否为空? 类型
 ----------------------------------------- -------- ---------------
 SID                                       NOT NULL NUMBER(4)
 PID                                                VARCHAR2(4)
 QUANTITY                                           NUMBER(4)
 SDATE                                              DATESQL> desc products;
 名称                                      是否为空? 类型
 ----------------------------------------- -------- --------------
 PID                                       NOT NULL VARCHAR2(5)
 PNAME                                              VARCHAR2(20)
 PTYPE                                              VARCHAR2(10)
 PLACE                                              VARCHAR2(30)
 PDATE                                              DATE
 VALIDITY                                           NUMBER(4)
 INPRICE                                            NUMBER(7,2)
 SALPRICE                                           NUMBER(7,2)
 BARGAINPRICE                                       NUMBER(7,2)
 QUANTITY                                           NUMBER(7)
 CID                                                VARCHAR2(5)

Answer 1

create or replace trigger sales_products
after insert on sales
begin
  update products set quantity=quantity-:new.quantity where pid=:new.pid;
end;

Answer 2

  1  create or replace trigger sales_products
  2  after insert on sales
  3  begin
  4     update products set quantity=quantity-:new.quantity where pid=:new.pid;
  5* end;
SQL> /
create or replace trigger sales_products
                          *
第 1 行出现错误:
ORA-04082: NEW 或 OLD 引用不允许在表级触发器中

Answer 3

create or replace trigger sales_products
before insert on sales
for each row --少了这个
begin
  update products set quantity=quantity-:new.quantity where pid=:new.pid;
end;

Answer 4

加个  for each row