MySQL 8.0

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select version();

version()

8.0.36

CREATE TABLE users (
  id int unsigned NOT NULL PRIMARY KEY,
  name varchar(255) NOT NULL
);

ALTER TABLE users ADD start datetime DEFAULT (DATE_SUB(now(), INTERVAL -1 DAY)) NOT NULL;

Records: 0  Duplicates: 0  Warnings: 0

insert into users (id, name) values (1, 'usera'), (2, 'usera');

Records: 2  Duplicates: 0  Warnings: 0

ALTER TABLE users ADD anotherDate datetime DEFAULT (now()) NOT NULL; -- This errors

Records: 2  Duplicates: 0  Warnings: 0

SELECT * FROM users;

id
name
start
anotherDate

1
usera
2024-11-15 07:07:51
2024-11-14 07:07:51

2
usera
2024-11-15 07:07:51
2024-11-14 07:07:51

id	name	start	anotherDate
1	usera	2024-11-15 07:07:51	2024-11-14 07:07:51
2	usera	2024-11-15 07:07:51	2024-11-14 07:07:51