mysql5.6 timestamp 变化，数据库版本升级到5.6需要注意此字段
1、版本，实测环境为centos6.6+mysql 5.6.25 社区版64bit
select @@version;
+------------+
| @@version |
+------------+
| 5.6.25-log |
+------------+
2、系统参数应设置为on ,如下图：
show variables like '%timestamp%';
+---------------------------------+-------------------+
| Variable_name | Value |
+---------------------------------+-------------------+
| explicit_defaults_for_timestamp | ON |
| timestamp | 1438824047.023471 |
+---------------------------------+-------------------+
3、创建表
CREATE TABLE `timestamp3` (
-> `id` int(11) NOT NULL AUTO_INCREMENT,
-> `time1` timestamp NULL DEFAULT NULL,
-> `time2` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
-> `time3` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
-> PRIMARY KEY (`id`)
-> ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 ;
Query OK, 0 rows affected (0.00 sec)
4、插入数据，观察5.6版本timestamp有什么变化
1）insert into timestamp3 (id) values(1);
Query OK, 1 row affected (0.00 sec)
2） select * from timestamp3;
+----+-------+---------------------+---------------------+
| id | time1 | time2 | time3 |
+----+-------+---------------------+---------------------+
| 1 | NULL | 2015-08-06 09:44:07 | 2015-08-06 09:44:07 |
+----+-------+---------------------+---------------------+
1 row in set (0.00 sec)
5、观察变化
1）update timestamp3 set id=id+1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
2）select * from timestamp3;
+----+-------+---------------------+---------------------+
| id | time1 | time2 | time3 |
+----+-------+---------------------+---------------------+
| 2 | NULL | 2015-08-06 09:44:07 | 2015-08-06 09:45:18 |
+----+-------+---------------------+---------------------+
1 row in set (0.00 sec)
6、结论
TIMESTAMP如果没有显示声明NOT NULL，是允许NULL值的，可以直接设置改列为NULL，而没有默认填充行为。
TIMESTAMP不会默认分配DEFAULT CURRENT_TIMESTAMP 和 ON UPDATE CURRENT_TIMESTAMP属性。