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修改该参数后并重启库后，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
explicit_defaults_for_timestamp = 0
|
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|
CREATETABLE `helei` (
`id`
int
(10) UNSIGNED
NOT
NULL
AUTO_INCREMENT ,
`t1`
timestamp
NULL
DEFAULT
NULL
COMMENT
'null'
,
`t2`
timestamp
NOT
NULL
COMMENT
'not null'
,
`t3`
timestamp
NOT
NULL
ON
UPDATECURRENT_TIMESTAMP COMMENT
'not null update'
,
PRIMARYKEY (`id`)
)
;
|
insert into helei(t1,t2,t3) values(null,null,null);
mysql> select * from helei;
+------+------+---------------------+---------------------+
| id | t1 | t2 | t3 |
+------+------+---------------------+---------------------+
| 2 | NULL | 2016-06-27 09:33:00 | 2016-06-27 09:33:00 |
t2虽然没有ON UPDATECURRENT_TIMESTAMP ，但由于explicit_defaults_for_timestamp没有开启，插入NULL不报错，且也插入了当前的时间
explicit_defaults_for_timestamp = 1
insert into helei(t1,t2,t3) values(null,null,null);
[SQL]insert into helei(t1,t2,t3) values(null,null,null)
[Err] 1048 - Column 't2' cannot be null
这才是我想要的
本文转自 dbapower 51CTO博客，原文链接：http://blog.51cto.com/suifu/1783400，如需转载请自行联系原作者
