在更新时创建触发器以将旧值插入到MYSQL中的其他表中

Question

I have two tables. The first is my person table which has id, name, creation_date as values, I have a old_person table (id, name, modified_date) which I want to populate the value of person before it actually changes. How would I go about that? I have tried triggers but failed.

I tried as follows

create trigger Person_Trigger Update on person
before update
as
insert into old_person(id, name, modified) 
select id, new.name, getdate()
from person

It's giving me syntax errors...Not many Trigger references out there either, a little push would be greatly appreciated!

Answer 1

Have a look at the following example

SQL Fiddle DEMO

IO hade a bit of trouble myself, but from How to Create Triggers in MySQL there was a line that made me think

The first MySQL command we'll issue is a little unusual:

DELIMITER $$

Our trigger body requires a number of SQL commands separated by a semi-colon (;). To create the full trigger code we must change delimiter to something else — such as $$.

Finally, we set the delimiter back to a semi-colon:

DELIMITER ;

So in the SQL Fiddle I changed the query terminator to GO and that seemed top work.

CREATE TABLE person
(
  id INT,
  name varchar(20)
)
GO
CREATE TABLE old_person
(
  id INT,
  name varchar(20),
  modified DATETIME
)
GO
CREATE TRIGGER Person_Trigger before update on person
FOR EACH ROW BEGIN
  INSERT INTO old_person(id, name, modified) 
  VALUES (OLD.id, OLD.name, NOW());
END
GO



INSERT INTO person VALUES (1,'TADA')
GO

UPDATE person SET name = 'FOO'
GO

Answer 2

Try this:

DELIMITER \\
CREATE TRIGGER `Person_Trigger`
BEFORE UPDATE ON `Person`
FOR EACH ROW
BEGIN
DECLARE date_modified datetime;

SET date_modified = NOW();

INSERT INTO old_person(id, name, modified) 
VALUES (OLD.id, OLD.name, date_modified);
END\\

This syntax works for me on my own projects. You may also need to declare delimiters before you begin the trigger. Also if you want to use the NEW keyword it should be AFTER update. Switch to the OLD keyword if you are going to keep using BEFORE update on your trigger.