oracle 使用触发器更改插入值
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Change inserted value with trigger
提问by hepifish
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:
几周前我刚刚开始学习 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，我找到了很多答案，但没有很好（对我来说）。我真的不明白问题出在哪里。这是代码：
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;
采纳答案by Mureinik
In Oracle's trigger syntax the newly inserted record is referred to by :new, not new(notice the colon). Additionally, SETis 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:
在 Oracle 的触发器语法中，新插入的记录由:new, not new（注意冒号）引用。此外，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，但请注意，这些是用:=而不是=.
所以，你的触发器应该是：
CREATE OR REPLACE TRIGGER NumberOfBooks
BEFORE INSERT
ON book
FOR EACH ROW
BEGIN
IF :new.nobook < 10
THEN
:new.nobook := 10;
END IF;
END;
