MySQL学习笔记11
MySQL日期类型：
###㈠ DATE类型（年-月-日）
The DATE type is used for values with a date part but no time part. MySQL retrieves and displays DATE values in'YYYY-MM-DD' format. The supported range is '1000-01-01' to '9999-12-31'.
###㈡ DATETIME(年月日 小时分钟秒)
The DATETIME type is used for values that contain both date and time parts. MySQL retrieves and displaysDATETIME values in 'YYYY-MM-DD HH:MM:SS' format. The supported range is '1000-01-01 00:00:00' to '9999-12-31 23:59:59'.
DATETIME范围相对于TIMESTAMP范围更广，
'1000-01-01 00:00:00'to'9999-12-31 23:59:59'
###㈢ TIMESTAMP(年月日小时分钟秒)
The TIMESTAMP data type is used for values that contain both date and time parts. TIMESTAMP has a range of '1970-01-01 00:00:01' UTC to '2038-01-19 03:14:07' UTC.
TIMESTAMP选项如果不插入时间，则MySQL会自动调用系统时间写入数据
###㈣ TIME（小时:分钟:秒）
MySQL retrieves and displays TIME values in 'HH:MM:SS' format (or 'HHH:MM:SS' format for large hours values).TIME values may range from '-838:59:59' to '838:59:59'.
说明：小时部分可以是这么大，因为可以使用TIME类型不仅代表一个时间(必须小于24小时),而且可以表示运行时间或两个事件之间的时间间隔(可能大于24小时,甚至负数)。
==注意：==
TIME这一列如果存储缩写，需要注意mysql的解释方式。无效的时间值会被转换成'00:00:00' 。
'11:12' means '11:12:00', not '00:11:12'.
'12' and 12 are interpreted as '00:00:12'.
###㈤ YEAR
YEAR(4) and YEAR(2) differ in display format, but have the same range of values.
For 4-digit format, MySQL displays YEAR values in YYYY format, with a range of 1901 to 2155, or 0000.
For 2-digit format, MySQL displays only the last two (least significant) digits; for example, 70 (1970 or 2070) or 69 (2069).
无效的值将会被转换成'0000'.
案例：编写tb_article文章表，定义字段（id、title、description、addtime）
mysql> create table tb_article1 (
-> id int unsigned not null auto_increment,
-> title varchar(80),
-> description varchar(255),
-> addtime datetime,
-> primary key(id)
-> )engine=innodb default charset=utf8;
Query OK, 0 rows affected (0.02 sec)
mysql>
mysql> create table tb_article2 (
-> id int unsigned not null auto_increment,
-> title varchar(80),
-> description varchar(255),
-> addtime timestamp,
-> primary key(id)
-> )engine=innodb default charset=utf8;
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> desc tb_article1;
+-------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| title | varchar(80) | YES | | NULL | |
| description | varchar(255) | YES | | NULL | |
| addtime | datetime | YES | | NULL | |
+-------------+------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql> desc tb_article2;
+-------------+------------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+------------------+------+-----+-------------------+-----------------------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| title | varchar(80) | YES | | NULL | |
| description | varchar(255) | YES | | NULL | |
| addtime | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-------------+------------------+------+-----+-------------------+-----------------------------+
4 rows in set (0.00 sec)
我们看到timestamp有一个默认值。
mysql> insert into tb_article1 values (null,'mysql从入门到放弃','mysql很好很强大...',null);
Query OK, 1 row affected (0.00 sec)
mysql> insert into tb_article2 values (null,'mysql从入门到放弃','mysql很好很强大...',null);
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> select * from tb_article1;
+----+-------------------------+-------------------------+---------+
| id | title | description | addtime |
+----+-------------------------+-------------------------+---------+
| 1 | mysql从入门到放弃 | mysql很好很强大... | NULL |
+----+-------------------------+-------------------------+---------+
1 row in set (0.00 sec)
mysql> select * from tb_article2;
+----+-------------------------+-------------------------+---------------------+
| id | title | description | addtime |
+----+-------------------------+-------------------------+---------------------+
| 1 | mysql从入门到放弃 | mysql很好很强大... | 2023-09-24 01:46:14 |
+----+-------------------------+-------------------------+---------------------+
1 row in set (0.00 sec)
如果超过2038年，那么就不要使用timestamp。
入学时间：2017年，那可以使用year(4)；