1. 背景
* MySQL支持多种表示日期和时间的数据类型，如YEAR、TIME、DATETIME、TIMESTAMP等等……
* MySQL 5.6.4版本开始支持微秒(支持类型：TIMTE、DATETIME、TIMESTAMP, 微秒长度最大为6)
2. 日期与时间类型所属空间与表示范围
| 类型 | 5.6.4版本之前 占用字节 | 5.6.4版本之后 (包含5.6.3版本) 占用字节 | 表示范围 |
| DATETIME | 8 | 6+(微秒长度-1 )/2 | 1000-01-01 00:00:00 ~ 9999-12-31 23:59:59 |
| DATE | 3 | 3 | 1000-01-01 ~ 9999-12-31 |
| TIMESTAMP | 4 | 4+(微秒长度-1 )/2 | 1970-01-01 00:00:00 UTC ~ 2038-01-19 03:14:07 UTC |
| YEAR | 1 | 1 | YEAR(2): 1970 ~ 2070 YEAR(4): 1901 ~ 2155 |
| TIME | 3 | 3+(微秒长度-1 )/2 | -838:59:59 ~ 838:59:59 |
3. 日期与时间类型 "0" 值格式
| 类型 | Zero Value |
| DATETIME | '0000-00-00 00:00:00' |
| DATE | '0000-00-00' |
| TIMESTAMP | '0000-00-00 00:00:00' |
| YEAR | 0000 |
| TIME | '00:00:00' |
4. 日期与时间类型相关函数操作
* NOW() 获取语句开始执行的日期和时间，[ MySQL 5.6.3版本之后可以获取微秒 ]
mysql> SELECT NOW(); +---------------------+ | NOW() | +---------------------+ | 2017-06-27 09:00:13 | +---------------------+ 1 row in set (0.00 sec) mysql> SELECT NOW(6); +----------------------------+ | NOW(6) | +----------------------------+ | 2017-06-27 09:18:50.720849 | +----------------------------+ 1 row in set (0.00 sec)
* SYSDATE() 获取SYSDATE()函数执行的时间
mysql> SELECT SYSDATE(), SLEEP(2), SYSDATE(); +---------------------+----------+---------------------+ | SYSDATE() | SLEEP(2) | SYSDATE() | +---------------------+----------+---------------------+ | 2017-06-27 09:38:03 | 0 | 2017-06-27 09:38:05 | +---------------------+----------+---------------------+ 1 row in set (2.01 sec)
* CURDATE() 获取当前日期
mysql> SELECT CURDATE(); +------------+ | CURDATE() | +------------+ | 2017-06-27 | +------------+ 1 row in set (0.00 sec)
* CURTIME() 获取当前时间
mysql> SELECT CURTIME(); +-----------+ | CURTIME() | +-----------+ | 09:05:51 | +-----------+ 1 row in set (0.03 sec)
* ADDDATE() 增加日期
[ 在当前日期上增加 10 天 ]
mysql> SELECT CURDATE(), ADDDATE(CURDATE(), "10"); +------------+--------------------------+ | CURDATE() | ADDDATE(CURDATE(), "10") | +------------+--------------------------+ | 2017-06-27 | 2017-07-07 | +------------+--------------------------+ 1 row in set (0.02 sec)
* ADDTIME() 增加时间
[ 在当前时间上增加1天1小时1分1秒 ]
mysql> SELECT NOW(), ADDTIME(NOW(), '1 1:1:1'); +---------------------+---------------------------+ | NOW() | ADDTIME(NOW(), '1 1:1:1') | +---------------------+---------------------------+ | 2017-06-27 09:00:21 | 2017-06-28 10:01:22 | +---------------------+---------------------------+ 1 row in set (0.02 sec)
* DATE() 返回字符串中的日期
mysql> SELECT NOW(), DATE(NOW()); +---------------------+-------------+ | NOW() | DATE(NOW()) | +---------------------+-------------+ | 2017-06-27 09:07:18 | 2017-06-27 | +---------------------+-------------+ 1 row in set (0.00 sec)
* TIME() 返回字符串中的时间
mysql> SELECT NOW(), TIME(NOW()); +---------------------+-------------+ | NOW() | TIME(NOW()) | +---------------------+-------------+ | 2017-06-27 09:07:40 | 09:07:40 | +---------------------+-------------+ 1 row in set (0.01 sec)
* YEAR() 返回字符串中的年数
mysql> SELECT NOW(), YEAR(NOW()); +---------------------+-------------+ | NOW() | YEAR(NOW()) | +---------------------+-------------+ | 2017-06-27 09:12:39 | 2017 | +---------------------+-------------+ 1 row in set (0.00 sec)
* MONTH() 返回字符串中的月数
mysql> SELECT NOW(), MONTH(NOW()); +---------------------+--------------+ | NOW() | MONTH(NOW()) | +---------------------+--------------+ | 2017-06-27 09:13:09 | 6 | +---------------------+--------------+ 1 row in set (0.01 sec)
* DAY() 返回字符串中的日数
mysql> SELECT NOW(), DAY(NOW()); +---------------------+------------+ | NOW() | DAY(NOW()) | +---------------------+------------+ | 2017-06-27 09:12:08 | 27 | +---------------------+------------+ 1 row in set (0.01 sec)
* HOUR() 返回字符串中的小时数
mysql> SELECT NOW(), HOUR(NOW()); +---------------------+-------------+ | NOW() | HOUR(NOW()) | +---------------------+-------------+ | 2017-06-27 09:13:57 | 9 | +---------------------+-------------+ 1 row in set (0.00 sec)
* MINUTE() 返回字符串中的分钟数
mysql> SELECT NOW(), MINUTE(NOW()); +---------------------+---------------+ | NOW() | MINUTE(NOW()) | +---------------------+---------------+ | 2017-06-27 09:15:38 | 15 | +---------------------+---------------+ 1 row in set (0.00 sec)
* SECOND() 返回字符串中的秒数
mysql> SELECT NOW(), SECOND(NOW()); +---------------------+---------------+ | NOW() | SECOND(NOW()) | +---------------------+---------------+ | 2017-06-27 09:16:23 | 23 | +---------------------+---------------+ 1 row in set (0.02 sec)
* MICROSECOND() 返回字符串中的微秒数 [MySQL 5.6.3版本之后]
mysql> SELECT NOW(6), MICROSECOND(NOW(6)); +----------------------------+---------------------+ | NOW(6) | MICROSECOND(NOW(6)) | +----------------------------+---------------------+ | 2017-06-27 09:18:11.264125 | 264125 | +----------------------------+---------------------+ 1 row in set (0.01 sec)
* DATEDIFF() 日期相减运算
mysql> SELECT DATEDIFF('2017-06-29', '2017-06-09');
+--------------------------------------+
| DATEDIFF('2017-06-29', '2017-06-09') |
+--------------------------------------+
| 20 |
+--------------------------------------+
1 row in set (0.00 sec)
mysql> SELECT DATEDIFF('2017-06-29', '2017-07-09');
+--------------------------------------+
| DATEDIFF('2017-06-29', '2017-07-09') |
+--------------------------------------+
| -10 |
+--------------------------------------+
1 row in set (0.03 sec)* DAYNAME() 返回工作日的英文名称
mysql> SELECT CURDATE(), DAYNAME(CURDATE()); +------------+--------------------+ | CURDATE() | DAYNAME(CURDATE()) | +------------+--------------------+ | 2017-06-27 | Tuesday | +------------+--------------------+ 1 row in set (0.01 sec)
* MONTHNAME() 返回月的英文名称
mysql> SELECT CURDATE(), MONTHNAME(CURDATE()); +------------+----------------------+ | CURDATE() | MONTHNAME(CURDATE()) | +------------+----------------------+ | 2017-06-27 | June | +------------+----------------------+ 1 row in set (0.01 sec)
* PERIOD_DIFF() 月数相减运算 [ 格式是YYYYMM或者YYMM ]
mysql> SELECT PERIOD_DIFF(201706, 201705); +-----------------------------+ | PERIOD_DIFF(201706, 201705) | +-----------------------------+ | 1 | +-----------------------------+ 1 row in set (0.00 sec) mysql> SELECT PERIOD_DIFF(201706, 201707); +-----------------------------+ | PERIOD_DIFF(201706, 201707) | +-----------------------------+ | -1 | +-----------------------------+ 1 row in set (0.00 sec)
…………等等，详情查看官网手册。
5. TIMESTAMP 和 DATETIME 区别 [ TIMESTAMP VS DATETIME]
* timestamp相比较datetime所占空间字节小。
* timestamp容易所支持的范围比timedate要小。 并且容易出现超出的情况
* timestamp受时区timezone的影响以及MYSQL版本和服务器的SQL MODE的影响, 而datetime不受时区影响.
6. 时间影响实验
* 创建表 t_d
mysql> CREATE TABLE t_d( -> t TIMESTAMP, -> d DATETIME -> )ENGINE=INNODB CHARSET=utf8mb4; Query OK, 0 rows affected (0.09 sec)
* 查看时区
mysql> show variables like '%zone%'; +------------------+--------+ | Variable_name | Value | +------------------+--------+ | system_time_zone | CST | | time_zone | SYSTEM | +------------------+--------+ 2 rows in set (0.02 sec)
* 插入数据
mysql> INSERT INTO t_d SELECT NOW(), NOW(); Query OK, 1 row affected (0.01 sec) Records: 1 Duplicates: 0 Warnings: 0
* 查看数据
mysql> SELECT * FROM t_d; +---------------------+---------------------+ | t | d | +---------------------+---------------------+ | 2017-06-27 09:44:13 | 2017-06-27 09:44:13 | +---------------------+---------------------+ 1 row in set (0.00 sec)
* 更新时区
mysql> set time_zone = '+0:00'; Query OK, 0 rows affected (0.00 sec)
* 再次查看数据
mysql> SELECT * FROM t_d; +---------------------+---------------------+ | t | d | +---------------------+---------------------+ | 2017-06-27 01:44:13 | 2017-06-27 09:44:13 | +---------------------+---------------------+ 1 row in set (0.01 sec)
7. 总结
以需求驱动技术，技术本身没有优略之分，只有业务之分。
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