MySQL Bugs: #107096: Conflicting statements re NULL and TIMESTAMP

Bug #107096	Conflicting statements re NULL and TIMESTAMP
Submitted:	22 Apr 2022 9:17	Modified:	25 Apr 2022 19:32
Reporter:	hanzhong zhang	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Documentation	Severity:	S2 (Serious)
Version:	ALL	OS:	Any (CentOS Linux release 7.9.2009 (Core) 3.10.0-1160.el7.x86_64)
Assigned to:	Jon Stephens	CPU Architecture:	Any ( Intel(R) Xeon(R) Silver 4210 CPU @ 2.20GHz)
Tags:	null, timestamp

Description:
In https://dev.mysql.com/doc/refman/5.7/en/problems-with-null.html ,The last line says " If you insert NULL into a TIMESTAMP column, the current date and time is inserted."

but the fact is "If you insert NULL into a TIMESTAMP column, the NULL is inserted."

How to repeat:
root@CentOS 16:58:  [test]>  create table test_null(id int auto_increment primary key ,`expire_at` timestamp NULL DEFAULT NULL COMMENT '具体失效时间',`expire_at_test` timestamp  COMMENT '具体失效时间')
    -> ;
Query OK, 0 rows affected (0.11 sec)

root@CentOS 16:59:  [test]> insert into test_null values(NULL,NULL,NULL);
Query OK, 1 row affected (0.02 sec)

root@CentOS 16:59:  [test]> select * from test_null;
+----+-----------+----------------+
| id | expire_at | expire_at_test |
+----+-----------+----------------+
|  1 | NULL      | NULL           |
+----+-----------+----------------+
1 row in set (0.00 sec)

Suggested fix:
Please update the official documents as soon as possible. Don't mislead people's children and attack the enthusiasm of beginners.

Hello hanzhong zhang,

Thank you for the report and feedback.

regards,
Umesh

你好！

The exact behaviour of NULL + TIMESTAMP is dependent on a number of factors, including the server SQL mode and the value of the explicit_defaults_for_timestamp system variable (note the default value changes from OFF in 5.7 to ON in MySQL 8.0).

I have updated this item in all versions of the Manual to make this clearer. Thanks for pointing this out!

Closed.