MariaDB 10.4

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CREATE TABLE people (
  `id`INT,
  `name` varchar(25),
  `updated_time` TIMESTAMP default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP 
);

INSERT INTO people
  (`id`, `name`)
VALUES
  (1,'test'),(2,'test3'),(3,'test2');
SELECT * FROM people;


id
name
updated_time


1
test
2021-06-28 22:24:56

2
test3
2021-06-28 22:24:56

3
test2
2021-06-28 22:24:56



ALTER TABLE people
     MODIFY 
            updated_time TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
ALTER TABLE people add created_at timestamp NULL default current_timestamp
SELECT * FROM people;


id
name
updated_time
created_at


1
test
2021-06-28 22:24:56
2021-06-28 22:24:56

2
test3
2021-06-28 22:24:56
2021-06-28 22:24:56

3
test2
2021-06-28 22:24:56
2021-06-28 22:24:56


UPDATE people SET created_at = NULL;
SELECT * FROM people;


id
name
updated_time
created_at


1
test
2021-06-28 22:24:56
null

2
test3
2021-06-28 22:24:56
null

3
test2
2021-06-28 22:24:56
null


ALTER TABLE people
     MODIFY 
            updated_time TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP
INSERT INTO people
  (`id`, `name`)
VALUES
  (4,'test')
SELECT * FROM people;


id
name
updated_time
created_at


1
test
2021-06-28 22:24:56
null

2
test3
2021-06-28 22:24:56
null

3
test2
2021-06-28 22:24:56
null

4
test
2021-06-28 22:24:56
2021-06-28 22:24:56

id	name	updated_time
1	test	2021-06-28 22:24:56
2	test3	2021-06-28 22:24:56
3	test2	2021-06-28 22:24:56

id	name	updated_time	created_at
1	test	2021-06-28 22:24:56	null
2	test3	2021-06-28 22:24:56	null
3	test2	2021-06-28 22:24:56	null