Triggers Oracle sql在插入/更新时触发以计算2个值并更新第三个值

我想创建一个触发器，通过计算2个值来更新行，并更新第三个值：

CREATE TABLE Customers (
    Cust_ID INTEGER PRIMARY KEY,
    Dates TIMESTAMP WITH LOCAL TIME ZONE,
    Quantity dec(7,2) NOT NULL,
    Price_per_item dec(7,2) NOT NULL,
    Total_price dec(7,2)
);

我已经这样做了：

CREATE OR REPLACE TRIGGER cust_after_insert AFTER INSERT 
ON Customers
FOR EACH ROW
BEGIN
    UPDATE Customers
    SET 
    DATES = CURRENT_TIMESTAMP,
    Total_price = Quantity * Price_per_item;
END;

我遇到了一些错误，我试图同时查看和编辑表

我也试过：

CREATE SEQUENCE cust_Seq START WITH 1 INCREMENT BY 1;
CREATE OR REPLACE TRIGGER cust_trig BEFORE INSERT ON Customers
FOR EACH ROW
BEGIN
  SELECT cust_Seq.nextval INTO :new.Fuel_ID FROM dual;
  SELECT CURRENT_TIMESTAMP INTO :new.DATES FROM dual;
  SELECT Quantity * Price_per_item INTO :new.Total_price FROM dual;
END;
/

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我更喜欢第二种选择，如果更新也会发生，我需要一些东西。

第二种方法方向正确，但需要一些调整来处理总价计算和处理更新：

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你会犯什么错误？某些类型的错误无助于调试问题。谢谢这是完美的，只是一个小的打字结束我需要的是结束，如果，谢谢@阿提拉：谢谢你注意到终端ID的错误-修正了。

CREATE SEQUENCE cust_Seq START WITH 1 INCREMENT BY 1;
CREATE OR REPLACE TRIGGER cust_trig BEFORE INSERT OR UPDATE ON Customers
FOR EACH ROW
BEGIN
  IF INSERTING THEN
    SELECT cust_Seq.nextval INTO :new.Fuel_ID FROM dual;
    SELECT CURRENT_TIMESTAMP INTO :new.DATES FROM dual;
  END IF;
  :new.Total_price :=  :new.Quantity * :new.Price_per_item;
END;
/