我正在写一个触发器，我正在用一堵墙压碎它，因为我需要将另一个表中的值保存在一个变量中，然后将该值减到另一个表的一列中，我正在使用一个触发器，但它不起作用：(
这是我的密码：

create or replace trigger tg_update_total_new_product
after insert on detalle_comanda 
for each row
declare
    var_precio numeric;
begin
    var_precio := (select precio from producto where id=:new.producto_id);
     update comanda set precuenta=precuenta+var_precio where id=:new.comanda_id;
END;

错误代码如下：

Trigger TG_UPDATE_TOTAL_NEW_PRODUCT compiled

LINE/COL  ERROR
--------- -------------------------------------------------------------
4/20      PLS-00103: Encountered the symbol "SELECT" when expecting one of the following:     ( - + case mod new not null <an identifier>    <a double-quoted delimited-identifier> <a bind variable>    continue avg count current exists max min prior sql stddev    sum variance execute forall merge time timestamp interval    date <a string literal with character set specification>    <a number> <a single-quoted SQL string> pipe    <an alternatively-quoted string literal with character set specification>    <an alternat
4/73      PLS-00103: Encountered the symbol ")" when expecting one of the following:     . ( * @ % & - + ; / at for mod remainder rem    <an exponent (**)> and or group having intersect minus order    start union where connect || indicator multiset 
6/4       PLS-00103: Encountered the symbol "end-of-file" when expecting one of the following:     end not pragma final instantiable persistable order    overriding static member constructor map 
Errors: check compiler log

那张表是中间的，然后我在另一张表中有销售总额，我想，当有人添加一个产品时，总额被添加。。。我一直在想一个函数，或者一个视图，但是我不知道为什么这不起作用。。。请帮帮我！谢谢！