MySQL基础知识03数据类型日期时间相关类型
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1. DATE
DATE类型只包含日期，格式：‘YYYY-MM-DD‘。范围从‘0000-01-01‘到‘9999-12-31‘。其中年月日只能输入有效的年月日。
mysql> create table d1 ( id date primary key);
Query OK, 0 rows affected (0.02 sec)
mysql> show create table d1;
+-------+-------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-------------------------------------------------------------------------------------------------------+
| d1 | CREATE TABLE `d1` (
`id` date NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> insert into d1 values (‘0001-01-01‘);
Query OK, 1 row affected (0.01 sec)
mysql> select * from d1;
+------------+
| id |
+------------+
| 0001-01-01 |
+------------+
1 row in set (0.00 sec)
MySQL将对日期的年月日进行合法性校验。
mysql> insert into d1 values (‘2017-02-29‘);
ERROR 1292 (22007): Incorrect date value: ‘2017-02-29‘ for column ‘id‘ at row 1
mysql> insert into d1 values (‘2017-02-28‘);
Query OK, 1 row affected (0.01 sec)
年的范围为0000到9999。
ERROR 1292 (22007): Incorrect date value: ‘20170-02-28‘ for column ‘id‘ at row 1
mysql> insert into d1 values (‘10000-02-28‘);
ERROR 1292 (22007): Incorrect date value: ‘10000-02-28‘ for column ‘id‘ at row 1
mysql> insert into d1 values (‘9999-02-28‘);
Query OK, 1 row affected (0.00 sec)
2. TIME
时间类型使用TIME表示。格式‘HH:MM:SS‘。
mysql> create table d2 ( id time primary key);
Query OK, 0 rows affected (0.04 sec)
mysql> show create table d2;
+-------+-------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-------------------------------------------------------------------------------------------------------+
| d2 | CREATE TABLE `d2` (
`id` time NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> insert into d2 values (‘00:00:00‘);
Query OK, 1 row affected (0.00 sec)
mysql> insert into d2 values (‘23:59:59‘);
Query OK, 1 row affected (0.01 sec)
mysql> insert into d2 values (‘24:00:00‘);
Query OK, 1 row affected (0.01 sec)
mysql> insert into d2 values (‘25:00:00‘);
Query OK, 1 row affected (0.02 sec)
mysql> insert into d2 values (‘00:60:60‘);
ERROR 1292 (22007): Incorrect time value: ‘00:60:60‘ for column ‘id‘ at row 1
mysql> insert into d2 values (‘00:00:60‘);
ERROR 1292 (22007): Incorrect time value: ‘00:00:60‘ for column ‘id‘ at row 1
mysql> select * from d2;
+----------+
| id |
+----------+
| 00:00:00 |
| 23:59:59 |
| 24:00:00 |
| 25:00:00 |
+----------+
4 rows in set (0.00 sec)
TIME类型的取值范围为：‘00:00:00‘到‘838:59:59‘。
mysql> insert into d2 values (‘838:59:59‘);
Query OK, 1 row affected (0.01 sec)
mysql> insert into d2 values (‘839:00:00‘);
ERROR 1292 (22007): Incorrect time value: ‘839:00:00‘ for column ‘id‘ at row 1
3. DATETIME
格式：‘YYYY-MM-DD HH:MM:SS‘。
范围：‘0000-01-01 00:00:00‘到‘9999-12-31 23:59:59‘。
mysql> create table d3 ( id datetime primary key);
Query OK, 0 rows affected (0.03 sec)
mysql> insert into d3 values (‘0000-01-01 00:00:00‘);
Query OK, 1 row affected (0.01 sec)
DATETIME中的年月日时分秒只能是合法的取值。其中小时不能超过23。
mysql> insert into d3 values (‘0000-01-01 24:00:00‘);
ERROR 1292 (22007): Incorrect datetime value: ‘0000-01-01 24:00:00‘ for column ‘id‘ at row 1
DATETIME类型的列可以显式指定默认值和更新时自动更新为当前时间。
mysql> create table d9 ( id int primary key,v1 datetime default current_timestamp on update current_timestamp);
Query OK, 0 rows affected (0.06 sec)
mysql> show create table d9;
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| d9 | CREATE TABLE `d9` (
`id` int(11) NOT NULL,
`v1` datetime DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> insert into d9 values (1);
ERROR 1136 (21S01): Column count doesn‘t match value count at row 1
mysql> insert into d9 (id) values (1);
Query OK, 1 row affected (0.02 sec)
mysql> select * from d9;
+----+---------------------+
| id | v1 |
+----+---------------------+
| 1 | 2017-09-01 12:37:12 |
+----+---------------------+
1 row in set (0.00 sec)
mysql> update d9 set id=2;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from d9;
+----+---------------------+
| id | v1 |
+----+---------------------+
| 2 | 2017-09-01 12:37:28 |
+----+---------------------+
1 row in set (0.01 sec)
4. TIMESTAMP
格式：‘YYYY-MM-DD HH:MM:SS‘。
范围：‘0000-01-01 00:00:00‘到‘9999-12-31 23:59:59‘。
mysql> create table d5 (id timestamp primary key);
Query OK, 0 rows affected (0.03 sec)
mysql> show create table d5;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| d5 | CREATE TABLE `d5` (
`id` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> insert into d5 values ();
Query OK, 1 row affected (0.01 sec)
mysql> select * from d5;
+---------------------+
| id |
+---------------------+
| 2017-09-01 12:15:16 |
+---------------------+
1 row in set (0.00 sec)
TIMESTAMP与DATETIME类型的区别：
(1)TIMESTAMP的默认值为CURRENT_TIMESTAMP，即当前时间。
在定义列时，默认情况下具备以下属性：
DEFAULT CURRENT_TIMESTAMP
而DATETIME类型则默认值为NULL，但是可以显式的指定为DEFAULT CURRENT_TIMESTAMP。
(2)TIMESTAMP类型的列在行数据更新时，默认情况下自动更新为当前时间。
在定义列时，默认情况下具备以下属性：
ON UPDATE CURRENT_TIMESTAMP,
而DATETIME类型则默认情况下并不自动更新，但是可以显式的指定ON UPDATE CURRENT_TIMESTAMP属性。
(3)TIMESTAMP类型的列在默认情况下为NOT NULL，如果需要赋值为NULL则必须显式定义为NULL属性。 DATETIME类型在默认情况下为NULL。
上述自动赋予的默认值和默认更新值仅仅对于数据表中第1个timestamp字段有效。
如果存在多个timestamp字段，则会报错：
mysql> create table d6 ( id int primary key,v1 datetime, v2 timestamp, v3 timestamp);
ERROR 1067 (42000): Invalid default value for ‘v3‘
此时需要显式的定义其它timestamp字段的default属性和on update属性。
mysql> create table d6 ( id int primary key,v1 datetime, v2 timestamp, v3 timestamp default current_timestamp on update current_timestamp);
Query OK, 0 rows affected (0.03 sec)
mysql> show create table d6;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| d6 | CREATE TABLE `d6` (
`id` int(11) NOT NULL,
`v1` datetime DEFAULT NULL,
`v2` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
`v3` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
TIMESTAMP类型在默认情况下的DEFAULT值是否定义为CURRENT_TIMESTAMP，以及ON UPDATE属性是否定义为CURRENT_TIMESTAMP，可以通过全局变量来控制：
mysql> show variables like ‘%timestamp%‘;
+---------------------------------+-------------------+
| Variable_name | Value |
+---------------------------------+-------------------+
| explicit_defaults_for_timestamp | OFF |
| log_timestamps | UTC |
| timestamp | 1504241030.617255 |
+---------------------------------+-------------------+
3 rows in set (0.16 sec)
explicit_defaults_for_timestamp 这个全局变量默认情况下为OFF，即不需要显式定义TIMESTAMP的默认值；如果修改为ON，则不会在定义数据表时自动加上DEFAULT和ON UPDATE属性。
mysql> set explicit_defaults_for_timestamp=on;
Query OK, 0 rows affected (0.05 sec)
mysql> create table d11 ( id timestamp primary key);
Query OK, 0 rows affected (0.05 sec)
mysql> show create table d11;
+-------+-------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-------------------------------------------------------------------------------------------------------------+
| d11 | CREATE TABLE `d11` (
`id` timestamp NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
5. 日期时间相关函数
(1)取得当前日期和时间。
now()取得当前日期和时间。
current_timestamp()取得当前日期和时间。
mysql> select now(), current_timestamp() ;
+---------------------+---------------------+
| now() | current_timestamp() |
+---------------------+---------------------+
| 2017-09-01 12:39:50 | 2017-09-01 12:39:50 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select current_timestamp ;
+---------------------+
| current_timestamp |
+---------------------+
| 2017-09-01 12:40:01 |
+---------------------+
1 row in set (0.00 sec)
now()函数必须是函数调用的形式。
mysql> select now ;
ERROR 1054 (42S22): Unknown column ‘now‘ in ‘field list‘
(2)独立取得当前日期和时间。
curdate()取得当前日期，curtime()取得当前时间。
mysql> select curdate(),curtime();
+------------+-----------+
| curdate() | curtime() |
+------------+-----------+
| 2017-09-01 | 13:34:14 |
+------------+-----------+
1 row in set (0.00 sec)
(3)取得指定日期时间的年月日时分秒的值。
mysql> select now(),year(now()), month(now()),day(now()), hour(now()),minute(now()),second(now());
+---------------------+-------------+--------------+------------+-------------+---------------+---------------+
| now() | year(now()) | month(now()) | day(now()) | hour(now()) | minute(now()) | second(now()) |
+---------------------+-------------+--------------+------------+-------------+---------------+---------------+
| 2017-09-01 13:48:26 | 2017 | 9 | 1 | 13 | 48 | 26 |
+---------------------+-------------+--------------+------------+-------------+---------------+---------------+
1 row in set (0.00 sec)
(4)等待一段时间。
sleep()函数提供了等待指定秒数的功能。
mysql> select now(); select sleep(11); select now();
+---------------------+
| now() |
+---------------------+
| 2017-09-01 13:54:07 |
+---------------------+
1 row in set (0.00 sec)
+-----------+
| sleep(11) |
+-----------+
| 0 |
+-----------+
1 row in set (11.00 sec)
+---------------------+
| now() |
+---------------------+
| 2017-09-01 13:54:18 |
+---------------------+
1 row in set (0.00 sec)
(5)sysdate。
sysdate()取得当前日期和时间。
now()函数返回的是语句开始执行时系统当前时间；而sysdate()函数返回的是函数执行时系统当前时间。
mysql> select now(), sleep(3), now();
+---------------------+----------+---------------------+
| now() | sleep(3) | now() |
+---------------------+----------+---------------------+
| 2017-09-01 14:01:34 | 0 | 2017-09-01 14:01:34 |
+---------------------+----------+---------------------+
1 row in set (3.00 sec)
可以看到两个now()返回的值相同，因为都是SELECT语句开始执行时的时间。
mysql> select sysdate(),sleep(3),sysdate();
+---------------------+----------+---------------------+
| sysdate() | sleep(3) | sysdate() |
+---------------------+----------+---------------------+
| 2017-09-01 14:01:49 | 0 | 2017-09-01 14:01:52 |
+---------------------+----------+---------------------+
1 row in set (3.01 sec)
两个sysdate()返回的时间并不相同，相隔了3秒钟。
6. 两位数年份
对于日期相关类型，如果输入两位数年份，则根据年份所在的范围识别为20XX或19XX。
(1)00到69：结果为20XX。
(2)70到99：结果为19XX。
mysql> select cast( ‘17-09-01‘ as date) as "17-09-01", cast(‘69-09-01‘ as date) as "69-09-01" , cast(‘70-09-01‘ as date ) as "70-09-01";
+------------+------------+------------+
| 17-09-01 | 69-09-01 | 70-09-01 |
+------------+------------+------------+
| 2017-09-01 | 2069-09-01 | 1970-09-01 |
+------------+------------+------------+
1 row in set (0.00 sec)
7. 微秒
对于时间相关类型TIME,TIMESTAMP,DATETIME，MySQL提供了微秒的表达方式。
mysql> select cast( ‘2017-09-01 13:51:25.123456‘ as datetime(6));
+-----------------------------------------------------+
| cast( ‘2017-09-01 13:51:25.123456‘ as datetime(6)) |
+-----------------------------------------------------+
| 2017-09-01 13:51:25.123456 |
+-----------------------------------------------------+
1 row in set (0.00 sec)
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