MySQL基础知识04数据类型日期时间的格式转换
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1. UNIX_TIMESTAMP
mysql提供了UNIX_TIMESTAMP()函数，用于计算自从1970-01-01 08:00:00以来所经过的秒数。此处开始时间是1970-01-01 08:00:00，而不是1970-01-01 00:00:00。对于早于1970-01-01 08:00:00的时间，返回值都为0。这个相对时间单位为秒，支持小数。
mysql> select unix_timestamp();
+------------------+
| unix_timestamp() |
+------------------+
| 1504246140 |
+------------------+
1 row in set (0.00 sec)
mysql> select unix_timestamp(‘1970-01-01 00:00:00‘);
+---------------------------------------+
| unix_timestamp(‘1970-01-01 00:00:00‘) |
+---------------------------------------+
| 0 |
+---------------------------------------+
1 row in set (0.00 sec)
mysql> select unix_timestamp(‘1970-01-01 01:00:00‘);
+---------------------------------------+
| unix_timestamp(‘1970-01-01 01:00:00‘) |
+---------------------------------------+
| 0 |
+---------------------------------------+
1 row in set (0.00 sec)
mysql> select unix_timestamp(‘1970-01-01 08:00:00‘);
+---------------------------------------+
| unix_timestamp(‘1970-01-01 08:00:00‘) |
+---------------------------------------+
| 0 |
+---------------------------------------+
1 row in set (0.00 sec)
mysql> select unix_timestamp(‘1970-01-01 08:00:01‘);
+---------------------------------------+
| unix_timestamp(‘1970-01-01 08:00:01‘) |
+---------------------------------------+
| 1 |
+---------------------------------------+
1 row in set (0.00 sec)
mysql> select unix_timestamp(‘1970-01-01 08:00:02‘);
+---------------------------------------+
| unix_timestamp(‘1970-01-01 08:00:02‘) |
+---------------------------------------+
| 2 |
+---------------------------------------+
1 row in set (0.00 sec)
mysql> select unix_timestamp(‘1970-01-02 00:00:00‘);
+---------------------------------------+
| unix_timestamp(‘1970-01-02 00:00:00‘) |
+---------------------------------------+
| 57600 |
+---------------------------------------+
1 row in set (0.00 sec)
mysql> select unix_timestamp(‘1970-01-03 00:00:00‘);
+---------------------------------------+
| unix_timestamp(‘1970-01-03 00:00:00‘) |
+---------------------------------------+
| 144000 |
+---------------------------------------+
1 row in set (0.00 sec)
unix_timestamp()函数支持小数，但最多保留6位小数。
mysql> select unix_timestamp(‘1970-01-01 08:00:02.123456‘);
+----------------------------------------------+
| unix_timestamp(‘1970-01-01 08:00:02.123456‘) |
+----------------------------------------------+
| 2.123456 |
+----------------------------------------------+
1 row in set (0.00 sec)
mysql> select unix_timestamp(‘1970-01-01 08:00:02.123456789‘);
+-------------------------------------------------+
| unix_timestamp(‘1970-01-01 08:00:02.123456789‘) |
+-------------------------------------------------+
| 2.123457 |
+-------------------------------------------------+
1 row in set (0.00 sec)
2. FROM_UNIXTIME
FROM_UNIXTIME()函数将自1970-01-01 08:00:00以来的秒数，转化为标准的字符串时间戳格式。
mysql> select from_unixtime( 0 );
+---------------------+
| from_unixtime( 0 ) |
+---------------------+
| 1970-01-01 08:00:00 |
+---------------------+
1 row in set (0.00 sec)
mysql> select from_unixtime( 1 );
+---------------------+
| from_unixtime( 1 ) |
+---------------------+
| 1970-01-01 08:00:01 |
+---------------------+
1 row in set (0.00 sec)
mysql> select from_unixtime( 1.123456 );
+----------------------------+
| from_unixtime( 1.123456 ) |
+----------------------------+
| 1970-01-01 08:00:01.123456 |
+----------------------------+
1 row in set (0.00 sec)
FROM_UNIXTIME()函数支持日期时间字符串的格式化。
mysql> select from_unixtime( 1.123456 ,‘%Y-%m-%d %H:%i:%s‘);
+-----------------------------------------------+
| from_unixtime( 1.123456 ,‘%Y-%m-%d %H:%i:%s‘) |
+-----------------------------------------------+
| 1970-01-01 08:00:01 |
+-----------------------------------------------+
1 row in set (0.00 sec)
3. DATE_FORMAT
将日期和时间相关类型转化为指定格式的字符串。
mysql> select date_format( now(),‘%Y-%m-%d %H:%i:%s‘);
+-----------------------------------------+
| date_format( now(),‘%Y-%m-%d %H:%i:%s‘) |
+-----------------------------------------+
| 2017-09-01 14:35:22 |
+-----------------------------------------+
1 row in set (0.00 sec)
4. SEC_TO_TIME
SEC_TO_TIME()函数将秒数转化为时间。
mysql> select sec_to_time(0),sec_to_time(1),sec_to_time(3600),sec_to_time(36000),sec_to_time(360000);
+----------------+----------------+-------------------+--------------------+---------------------+
| sec_to_time(0) | sec_to_time(1) | sec_to_time(3600) | sec_to_time(36000) | sec_to_time(360000) |
+----------------+----------------+-------------------+--------------------+---------------------+
| 00:00:00 | 00:00:01 | 01:00:00 | 10:00:00 | 100:00:00 |
+----------------+----------------+-------------------+--------------------+---------------------+
1 row in set (0.00 sec)
5. TIME_TO_SEC
TIME_TO_SEC()函数将时间转化为秒数。
mysql> select time_to_sec(‘00:00:00‘), time_to_sec(‘00:00:01‘),time_to_sec(‘01:00:00‘),time_to_sec(‘100:00:00‘);
+-------------------------+-------------------------+-------------------------+--------------------------+
| time_to_sec(‘00:00:00‘) | time_to_sec(‘00:00:01‘) | time_to_sec(‘01:00:00‘) | time_to_sec(‘100:00:00‘) |
+-------------------------+-------------------------+-------------------------+--------------------------+
| 0 | 1 | 3600 | 360000 |
+-------------------------+-------------------------+-------------------------+--------------------------+
1 row in set (0.00 sec)
6. TIMESTAMPDIFF
TIMESTAMPDIFF()函数用于计算两个时间戳之间的差异，单位可以指定为年月日时分秒中的任何一个，也可以指定为微秒。
mysql> select timestampdiff(YEAR,‘2017-09-01‘, ‘2000-09-01‘);
+------------------------------------------------+
| timestampdiff(YEAR,‘2017-09-01‘, ‘2000-09-01‘) |
+------------------------------------------------+
| -17 |
+------------------------------------------------+
1 row in set (0.00 sec)
mysql> select timestampdiff(YEAR,‘2017-09-01‘, ‘2027-09-01‘);
+------------------------------------------------+
| timestampdiff(YEAR,‘2017-09-01‘, ‘2027-09-01‘) |
+------------------------------------------------+
| 10 |
+------------------------------------------------+
1 row in set (0.00 sec)
mysql> select timestampdiff(MONTH,‘2017-09-01‘, ‘2027-09-01‘);
+-------------------------------------------------+
| timestampdiff(MONTH,‘2017-09-01‘, ‘2027-09-01‘) |
+-------------------------------------------------+
| 120 |
+-------------------------------------------------+
1 row in set (0.00 sec)
mysql> select timestampdiff(DAY,‘2017-09-01‘, ‘2017-10-01‘);
+-----------------------------------------------+
| timestampdiff(DAY,‘2017-09-01‘, ‘2017-10-01‘) |
+-----------------------------------------------+
| 30 |
+-----------------------------------------------+
1 row in set (0.00 sec)
mysql> select timestampdiff(HOUR,‘2017-09-01‘, ‘2017-10-01‘);
+------------------------------------------------+
| timestampdiff(HOUR,‘2017-09-01‘, ‘2017-10-01‘) |
+------------------------------------------------+
| 720 |
+------------------------------------------------+
1 row in set (0.00 sec)
mysql> select timestampdiff(MINUTE,‘2017-09-01‘, ‘2017-10-01‘);
+--------------------------------------------------+
| timestampdiff(MINUTE,‘2017-09-01‘, ‘2017-10-01‘) |
+--------------------------------------------------+
| 43200 |
+--------------------------------------------------+
1 row in set (0.00 sec)
mysql> select timestampdiff(SECOND,‘2017-09-01‘, ‘2017-10-01‘);
+--------------------------------------------------+
| timestampdiff(SECOND,‘2017-09-01‘, ‘2017-10-01‘) |
+--------------------------------------------------+
| 2592000 |
+--------------------------------------------------+
1 row in set (0.00 sec)
mysql> select timestampdiff(MICROSECOND,‘2017-09-01‘, ‘2017-10-01‘);
+-------------------------------------------------------+
| timestampdiff(MICROSECOND,‘2017-09-01‘, ‘2017-10-01‘) |
+-------------------------------------------------------+
| 2592000000000 |
+-------------------------------------------------------+
1 row in set (0.00 sec)
mysql> select timestampdiff(MICROSECOND,‘2017-09-01 00:00:00.123456‘, ‘2017-09-01 00:00:01.000001‘);
+---------------------------------------------------------------------------------------+
| timestampdiff(MICROSECOND,‘2017-09-01 00:00:00.123456‘, ‘2017-09-01 00:00:01.000001‘) |
+---------------------------------------------------------------------------------------+
| 876545 |
+---------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
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