MySQL timestamp NOT NULL插入NULL的问题

Posted 2020-07-13

explicit_defaults_for_timestamp

mysql 5.6版本引入

explicit_defaults_for_timestamp

来控制对timestamp NULL值的处理

 

如果该参数不开启，则对timestamp NOT NULL插入NULL值，不报错，无warning，插入后的值为当前时间

如果在my.cnf中explicit_defaults_for_timestamp=1

那么插入该值的时候会报错提示该列can not be null

建议开启该值

mysql> show variables like ‘%explicit_defaults_for_timestamp%‘;
+---------------------------------+-------+
| Variable_name                   | Value |
+---------------------------------+-------+
| explicit_defaults_for_timestamp | OFF   |
+---------------------------------+-------+
1 row in set (0.00 sec)

mysql> show create table helei\G
*************************** 1. row ***************************
       Table: helei
Create Table: CREATE TABLE `helei` (
  `a` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.08 sec)

mysql> select * from helei;
Empty set (0.03 sec)

mysql> insert into helei values(NULL);
Query OK, 1 row affected (0.39 sec)

mysql> select * from helei;
+---------------------+
| a                   |
+---------------------+
| 2016-05-26 11:44:24 |
+---------------------+
1 row in set (0.03 sec)

可以看到

explicit_defaults_for_timestamp

插入的NULL值变为当前时间，并没有被NOT NULL所限制

且该值是无法动态修改的，必须重启库才可以变更

mysql> set global explicit_defaults_for_timestamp=0;

ERROR 1238 (HY000): Variable ‘explicit_defaults_for_timestamp‘ is a read only variable

我们在my.cnf并重启库后，可以看到null值已经不被允许插入了

mysql> select * from helei;
+---------------------+
| a                   |
+---------------------+
| 2016-05-26 11:44:24 |
| 2016-05-26 11:45:46 |
+---------------------+
2 rows in set (0.00 sec)

mysql> insert into helei values(null);
ERROR 1048 (23000): Column ‘a‘ cannot be null

mysql> insert into helei values(NULL);
ERROR 1048 (23000): Column ‘a‘ cannot be null

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