使用触发器更改插入的值 [英] Change inserted value with trigger

问题描述

几周前我才刚开始学习SQL，我正在尝试制作一个触发器，如果​​插入的值小于10，它会将插入的值更改为10.我现在搜索了4h，发现了很多答案，但没有一个好(对我来说).我真的不明白问题出在哪里. 这是代码:

I've just started to learn SQL a few weeks ago and I'm trying to make a trigger which changes the inserted value into 10 if it's smaller than 10. I searched for 4h now and I've found a lot of answers but none was good(for me). I really don't understand where the problem is. Here is the code:

CREATE OR REPLACE TRIGGER NumberOfBooks
BEFORE INSERT
ON Book
FOR EACH ROW
BEGIN 
  IF new.nobook < 10
  THEN
    SET new.nobook = 10;
  END IF;
  END;

推荐答案

在Oracle的触发器语法中，新插入的记录由:new而不是new引用(请注意冒号).另外，SET是更新语句的一部分，而不是设置字段值的方法-这些是通过简单的赋值完成的，但是请注意，这些是通过:=而不是=完成的.
因此，您的触发器应显示为:

In Oracle's trigger syntax the newly inserted record is referred to by :new, not new (notice the colon). Additionally, SET is a part of an update statement, not a way to set field values - those are done by simple assignments, but note that these are done with := rather than =.
So, your trigger should read:

CREATE OR REPLACE TRIGGER NumberOfBooks
    BEFORE INSERT
    ON book
    FOR EACH ROW
BEGIN
    IF :new.nobook < 10
    THEN
        :new.nobook := 10;
    END IF;
END;

这篇关于使用触发器更改插入的值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！