在mysql中：
- timestamp列如果没有显式定义为null，默认会被设置为not null属性。(其它的数据类型如果没有显式定义为not null，默认是可以为null的)。设置timestamp的列值为null，会自动存储为当前timestamp
- 表中的第一个timestamp列，如果没有定义为null、定义default值或者on update，会自动分配default current_timestamp和on update current_timestamp属性
- 表中第一个timestamp列之后的所有timestamp列，如果没有被定义为null、定义default值，会自动被指定默认值'0000-00-00 00:00:00'。在插入时，如果没有指定这些列的值，会自动指定为'0000-00-00 00:00:00'，且不会产生警告
1 mysql> create table timestamp_eg( 2 -> id int not null auto_increment, 3 -> time1 timestamp, 4 -> time2 timestamp, 5 -> time3 timestamp NOT NULL DEFAULT '2010-01-01 00:00:00', 6 -> time4 timestamp, 7 -> primary key(id)); 8 Query OK, 0 rows affected (0.01 sec) 9 10 mysql> insert into timestamp_eg(id) values(1); 11 Query OK, 1 row affected (0.00 sec) 12 13 mysql> select * from timestamp_eg; 14 +----+---------------------+---------------------+---------------------+---------------------+ 15 | id | time1 | time2 | time3 | time4 | 16 +----+---------------------+---------------------+---------------------+---------------------+ 17 | 1 | 2015-12-16 09:23:33 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 0000-00-00 00:00:00 | 18 +----+---------------------+---------------------+---------------------+---------------------+ 19 1 row in set (0.01 sec) 20 21 mysql> update timestamp_eg set id=2 where id=1; 22 Query OK, 1 row affected (0.02 sec) 23 Rows matched: 1 Changed: 1 Warnings: 0 24 25 mysql> select * from timestamp_eg; 26 +----+---------------------+---------------------+---------------------+---------------------+ 27 | id | time1 | time2 | time3 | time4 | 28 +----+---------------------+---------------------+---------------------+---------------------+ 29 | 2 | 2015-12-16 09:25:01 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 0000-00-00 00:00:00 | 30 +----+---------------------+---------------------+---------------------+---------------------+ 31 1 row in set (0.00 sec) 32 33 mysql> insert into timestamp_eg(id,time4) values(3,'2011-01-01 00:00:00'); 34 Query OK, 1 row affected (0.00 sec) 35 36 mysql> select * from timestamp_eg; 37 +----+---------------------+---------------------+---------------------+---------------------+ 38 | id | time1 | time2 | time3 | time4 | 39 +----+---------------------+---------------------+---------------------+---------------------+ 40 | 2 | 2015-12-16 09:25:01 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 0000-00-00 00:00:00 | 41 | 3 | 2015-12-16 09:28:04 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 2011-01-01 00:00:00 | 42 +----+---------------------+---------------------+---------------------+---------------------+ 43 2 rows in set (0.00 sec) 44 45 mysql> update timestamp_eg set id=4 where id=3; 46 Query OK, 1 row affected (0.00 sec) 47 Rows matched: 1 Changed: 1 Warnings: 0 48 49 mysql> select * from timestamp_eg; 50 +----+---------------------+---------------------+---------------------+---------------------+ 51 | id | time1 | time2 | time3 | time4 | 52 +----+---------------------+---------------------+---------------------+---------------------+ 53 | 2 | 2015-12-16 09:25:01 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 0000-00-00 00:00:00 | 54 | 4 | 2015-12-16 09:28:24 | 0000-00-00 00:00:00 | 2010-01-01 00:00:00 | 2011-01-01 00:00:00 | 55 +----+---------------------+---------------------+---------------------+---------------------+ 56 2 rows in set (0.00 sec) 57 58 mysql>
从MySQL5.6.6这种默认设置的方法被废弃了。在MySQL启动时会出现以下警告：
1 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. 2 Please use --explicit_defaults_for_timestamp server option (see 3 documentation for more details).
要想取消该警告，在启动mysql时，my.cnf中加入
1 [mysqld] 2 explicit_defaults_for_timestamp=true
修改该参数后，timestamp类型的列的处理方式也会发生变化：
- timestamp列如果没有显式定义为not null，则支持null属性。设置timestamp的列值为null，就不会被设置为current timestamp
- 不会自动分配default current_timestamp和on update current_timestamp属性，这些属性必须显式指定
- 声明为not null且没有显式指定默认值是没有默认值的。表中插入列，又没有给timestamp列赋值时，如果是严格sql模式，会抛出一个错误；如果严格sql模式没有启用，该列会赋值为’0000-00-00 00:00:00′，同时出现一个警告。（这和mysql处理其它时间类型数据一样，如datetime）
1 mysql> create table timestamp_02( 2 -> id int not null auto_increment, 3 -> time1 timestamp not null, 4 -> primary key(id) 5 -> ); 6 Query OK, 0 rows affected (0.03 sec) 7 8 mysql> insert into timestamp_02(id) values(1); 9 ERROR 1364 (HY000): Field 'time1' doesn't have a default value 10 mysql>