- TIMESTAMP列如果没有明确声明NULL属性，默认为NOT NULL。（而其他数据类型，如果没有显示声明为NOT NULL，则允许NULL值。）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，如果没有声明NULL属性、DEFAULT或者 ON UPDATE，会自动分配 DEFAULT CURRENT_TIMESTAMP和ON UPDATE CURRENT_TIMESTAMP 属性。
- 表中第二个TIMESTAMP列，如果没有声明为NULL或者DEFAULT子句，默认自动分配’0000-00-00 00:00:00′。插入行时没有指明改列的值，该列默认分配’0000-00-00 00:00:00′，且没有警告。
因为默认情况下充许为空,当插入值时,分两种情况：第一列与第二列情况 explicit_defaults_for_timestamp=false [默认值]
mysql> create table timestamp(id int not null auto_increment,time1 timestamp,time2 timestamp,primary key(id))engine=innodb; Query OK, 0 rows affected (0.27 sec) mysql> insert into timestamp(id) values(1); Query OK, 1 row affected (0.21 sec) mysql> select * from timestamp; +----+---------------------+---------------------+ | id | time1 | time2 | +----+---------------------+---------------------+ | 1 | 2016-07-02 17:12:28 | 0000-00-00 00:00:00 | +----+---------------------+---------------------+ 1 row in set (0.19 sec) mysql> mysql> show create table timestamp; CREATE TABLE `timestamp` ( `id` int(11) NOT NULL AUTO_INCREMENT, `time1` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `time2` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 2列TIMESTAMP未声明为NULL的默认行为
timestamp有两个属性，分别是CURRENT_TIMESTAMP 和ON UPDATE CURRENT_TIMESTAMP两种，使用情况分别如下： 1. CURRENT_TIMESTAMP 当要向数据库执行insert操作时，如果有个timestamp字段属性设为 CURRENT_TIMESTAMP，则无论这个字段有没有set值都插入当前系统时间 2. ON UPDATE CURRENT_TIMESTAMP 当执行update操作时，并且字段有ON UPDATE CURRENT_TIMESTAMP属性。则字段无论值有没有变化，它的值也会跟着更新为当前UPDATE操作时的时间。
从MySQL5.6.6开始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：
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[Warning] TIMESTAMP with implicit DEFAULT value is deprecated.Please use --explicit_defaults_for_timestamp server option(seedocumentation for more details). |
关闭警告，在my.cnf中加入
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[mysqld]explicit_defaults_for_timestamp=true |
重启MySQL后错误消失，这时TIMESTAMP的行为如下：
- 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。
mysql> create table timestamp1(id int not null auto_increment,time1 timestamp,time2 timestamp,primary key(id))engine=innodb; Query OK, 0 rows affected (0.11 sec) mysql> insert into timestamp1(id) values(1); Query OK, 1 row affected (0.18 sec) mysql> show create table timestamp1; CREATE TABLE `timestamp1` ( `id` int(11) NOT NULL AUTO_INCREMENT, `time1` timestamp NULL DEFAULT NULL, `time2` timestamp NULL DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 mysql> select * from timestamp1; +----+-------+-------+ | id | time1 | time2 | +----+-------+-------+ | 1 | NULL | NULL | +----+-------+-------+ 1 row in set (0.18 sec)
mysql> set sql_mode="STRICT_TRANS_TABLES"; Query OK, 0 rows affected (0.00 sec) mysql> create table timestamp4(id int not null auto_increment,time1 timestamp not null,time2 timestamp not null,primary key(id))engine=innodb; Query OK, 0 rows affected (0.03 sec) mysql> insert into timestamp4 select 1,"0000-00-00 00:00:00","0000-00-00 00:00:00"; Query OK, 1 row affected (0.17 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> insert into timestamp4 select 1,"0000-00-00 00:00:00","5"; ERROR 1292 (22007): Incorrect datetime value: '5' for column 'time2' at row 1 mysql> set sql_mode="STRICT_TRANS_TABLES,NO_ZERO_DATE"; Query OK, 0 rows affected, 1 warning (0.00 sec) mysql> insert into timestamp4 select 1,"0000-00-00 00:00:00","0000-00-00 00:00:00"; ERROR 1292 (22007): Incorrect datetime value: '0000-00-00 00:00:00' for column 'time1' at row 1
mysql> set sql_mode="STRICT_TRANS_TABLES,NO_ZERO_DATE,NO_ZERO_IN_DATE"; Query OK, 0 rows affected, 2 warnings (0.00 sec) mysql> insert into timestamp4 select 5,"2000-10-10 10:20:10","2000-10-10 10:20:00"; Query OK, 1 row affected (0.18 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> insert into timestamp4 select 7,"2000-10-00 10:20:10","2000-10-10 10:20:11"; 日期中不能有00 ERROR 1292 (22007): Incorrect datetime value: '2000-10-00 10:20:10' for column 'time1' at row 1
mysql> create table y( a int not null auto_increment primary key,b timestamp Default CURRENT_TIMESTAMP); 当有记录插入时,把当前日期与时间写入到 b字段中，但更新不会改变值 mysql> create table y1( a int not null auto_increment primary key,b timestamp on update CURRENT_TIMESTAMP); 当有记录插入时,NULL写入到B 字段中,当该行update时，b列值为当前更新时间值 mysql> create table y2( a int not null auto_increment primary key,b timestamp default current_timestamp on update CURRENT_TIMESTAMP); 当插入时,有一个默认值,随着当前行的更新,b列值也随着更新为当前更新时间 mysql> insert into y(a) values(null); Query OK, 1 row affected (0.17 sec) mysql> insert into y1(a) values(null); Query OK, 1 row affected (0.17 sec) mysql> insert into y2(a) values(null); Query OK, 1 row affected (0.17 sec) mysql> select * from y; +---+---------------------+ | a | b | +---+---------------------+ | 1 | 2016-07-02 18:56:59 | +---+---------------------+ 1 row in set (0.00 sec) mysql> select * from y1; +---+------+ | a | b | +---+------+ | 1 | NULL | +---+------+ 1 row in set (0.00 sec) mysql> select * from y2; +---+---------------------+ | a | b | +---+---------------------+ | 1 | 2016-07-02 18:57:08 | +---+---------------------+ 1 row in set (0.00 sec) mysql> update y set a=2 where a=1; Query OK, 1 row affected (0.20 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from y; +---+---------------------+ | a | b | +---+---------------------+ | 2 | 2016-07-02 18:56:59 | +---+---------------------+ 1 row in set (0.01 sec) mysql> update y1 set a=2 where a=1; Query OK, 1 row affected (0.17 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from y1; +---+---------------------+ | a | b | +---+---------------------+ | 2 | 2016-07-02 19:00:12 | +---+---------------------+ 1 row in set (0.00 sec) mysql> update y2 set a=2 where a=1; Query OK, 1 row affected (0.01 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from y2; +---+---------------------+ | a | b | +---+---------------------+ | 2 | 2016-07-02 19:00:35 | +---+---------------------+ 1 row in set (0.00 sec)
设置正常日期格式: 严格日期格式: set sql_mode="STRICT_TRANS_TABLES,NO_ZERO_DATE,NO_ZERO_IN_DATE";
手动指定默认值:
create table y2( a int not null auto_increment primary key,b timestamp default current_timestamp on update CURRENT_TIMESTAMP);