AFTER UPDATE trigger and ON UPDATE now(): new value <> persisted value

create table person

(

id bigint unsigned not null auto_increment primary key,

sno varchar(50) not null,

update_time DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP

);

create table person_id123 like person;

delimiter $$

CREATE TRIGGER school.person_AI_oak AFTER INSERT ON school.person

FOR EACH ROW

REPLACE INTO school.person_id123 (`id`, `sno`, `update_time`) VALUES (NEW.`id`, NEW.`sno`, NEW.`update_time`) $$

delimiter ;

delimiter $$

CREATE TRIGGER school.person_AD_oak AFTER DELETE ON school.person

FOR EACH ROW

DELETE FROM school.person_id123 WHERE (id) = (OLD.id) $$

delimiter ;

delimiter $$

CREATE TRIGGER school.person_AU_oak AFTER UPDATE ON school.person

FOR EACH ROW

BEGIN

INSERT IGNORE INTO school.person_id123 (`id`, `sno`, `update_time`) VALUES (OLD.`id`, OLD.`sno`, OLD.`update_time`) ;

UPDATE school.person_id123 SET `id`=NEW.`id`, `sno`=NEW.`sno`, `update_time`=NEW.`update_time` WHERE (id) = (OLD.id) ;

END $$

delimiter ;

insert into person(sno) values(100),(200);

select * from person;

--------------------------

id	sno	update_time

--------------------------

3	100	2025-12-08 18:47:14

4	200	2025-12-08 18:47:14

--------------------------

2 rows in set (0.00 sec)

select * from person_id123 ;

--------------------------

id	sno	update_time

--------------------------

3	100	2025-12-08 18:47:14

4	200	2025-12-08 18:47:14

--------------------------

2 rows in set (0.00 sec)

update person set sno='100' where id=3;

Query OK, 0 rows affected (0.00 sec)

Rows matched: 1 Changed: 0 Warnings: 0

select * from person;

--------------------------

id	sno	update_time

--------------------------

3	100	2025-12-08 18:47:14

4	200	2025-12-08 18:47:14

--------------------------

2 rows in set (0.00 sec)

select * from person_id123 ;

--------------------------

id	sno	update_time

--------------------------

3	100	2025-12-08 18:47:58	#time is updated, I don't want to update.

4	200	2025-12-08 18:47:14

--------------------------

2 rows in set (0.00 sec)