MySQL数据类型--------日期与时间类型实战
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DATETIME86+(微秒长度-1 )/21000-01-01 00:00:00 ~ 9999-12-31 23:59:59DATE331000-01-01 ~ 9999-12-31TIMESTAMP44+(微秒长度-1 )/21970-01-01 00:00:00 UTC ~ 2038-01-19 03:14:07 UTCYEAR11 YEAR(2): 1970 ~ 2070
YEAR(4): 1901 ~ 2155
TIME33+(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 ValueDATETIME'0000-00-00 00:00:00'DATE'0000-00-00'TIMESTAMP'0000-00-00 00:00:00'YEAR0000TIME'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> 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: 1Duplicates: 0Warnings: 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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