通过触发器自动填充描述列

Question

I would like to auto-populate the description column through trigger but I'm stuck in the inserting part, here is my code:

CREATE OR REPLACE TRIGGER "INSERT_MESSAGE" AFTER INSERT, UPDATE ON "A"
FOR EACH ROW
BEGIN
    SELECT "SEQ_A".NEXTVAL INTO :NEW.MESSAGE FROM DUAL
END;
/

There is a table "A" which has a column "MESSAGE", and the message will be generated into that column with a specific format: "Hi how are you?" How can I generate this text into that column when the trigger is activated? Thank you.

Answer 1

Logically you cannot change something after it's happened and there are a few syntax issues with your code. Try

CREATE OR REPLACE TRIGGER "INSERT_MESSAGE" before INSERT or UPDATE ON "A" 
FOR EACH ROW 
BEGIN 
SELECT “SEQ_A”.NEXTVAL INTO :NEW.MESSAGE FROM DUAL ;
END;