MySQL内置关于时间戳的计算和转换函数介绍
TIMESTAMP函数
语法：
TIMESTAMP(datetime_expr)
TIMESTAMP(datetime_expr,expr)
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说明：
一个参数时，是将datetime_expr转换成时间戳格式(timestamp)，两个参数时，是将datetime_expr转换成时间戳并加上expr
使用举例：
mysql> select timestamp(\'2019-07-20 08:00:00\');
+----------------------------------+
| timestamp(\'2019-07-20 08:00:00\') |
+----------------------------------+
| 2019-07-20 08:00:00 |
+----------------------------------+
1 row in set
mysql> select timestamp(\'2019-07-20 08:00:00\', \'01\');
+----------------------------------------+
| timestamp(\'2019-07-20 08:00:00\', \'01\') |
+----------------------------------------+
| 2019-07-20 08:00:01 |
+----------------------------------------+
1 row in set
mysql> select timestamp(\'2019-07-20 08:00:00\', \'01:01\');
+-------------------------------------------+
| timestamp(\'2019-07-20 08:00:00\', \'01:01\') |
+-------------------------------------------+
| 2019-07-20 09:01:00 |
+-------------------------------------------+
1 row in set
mysql> select timestamp(\'2019-07-20 08:00:00\', \'01:01:01\');
+----------------------------------------------+
| timestamp(\'2019-07-20 08:00:00\', \'01:01:01\') |
+----------------------------------------------+
| 2019-07-20 09:01:01 |
+----------------------------------------------+
1 row in set
mysql> select timestamp(\'2019-07-20 08:00:00\', \'10 01:01:01\');
+-------------------------------------------------+
| timestamp(\'2019-07-20 08:00:00\', \'10 01:01:01\') |
+-------------------------------------------------+
| 2019-07-30 09:01:01 |
+-------------------------------------------------+
1 row in set
mysql> select timestamp(\'2019-07-20 08:00:00\', \'01 10\');
+-------------------------------------------+
| timestamp(\'2019-07-20 08:00:00\', \'01 10\') |
+-------------------------------------------+
| 2019-07-21 18:00:00 |
+-------------------------------------------+
1 row in set
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TIMESTAMPDIFF函数
语法：
TIMESTAMPDIFF(interval,datetime_expr1,datetime_expr2)
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说明：
返回日期或日期时间表达式datetime_expr1 和datetime_expr2 之间的整数差。其结果的单位由interval 参数给出。该参数必须是以下值的其中一个：
FRAC_SECOND 表示间隔是毫秒
SECOND 秒
MINUTE 分钟
HOUR 小时
DAY 天
WEEK 星期
MONTH 月
QUARTER 季度
YEAR 年
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使用如下：
mysql> select TIMESTAMPDIFF(day,\'2019-07-10\',\'2019-07-20\');
+----------------------------------------------+
| TIMESTAMPDIFF(day,\'2019-07-10\',\'2019-07-20\') |
+----------------------------------------------+
| 10 |
+----------------------------------------------+
1 row in set
mysql> select TIMESTAMPDIFF(MINUTE,\'2019-07-15 09:00:00\',\'2019-07-20 19:00:00\');
+-------------------------------------------------------------------+
| TIMESTAMPDIFF(MINUTE,\'2019-07-15 09:00:00\',\'2019-07-20 19:00:00\') |
+-------------------------------------------------------------------+
| 7800 |
+-------------------------------------------------------------------+
1 row in set
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TIMESTAMPADD函数
语法：
TIMESTAMPADD(interval,int_expr,datetime_expr)
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说明：
将整型表达式int_expr添加到日期或日期时间表达式 datetime_expr中。式中的nterval和上文中列举的取值是一样的。
例如，int_expr为MINUTE时，是将datetime_expr时间增加int_expr分钟。
mysql> select TIMESTAMPADD(MINUTE,60,\'2019-07-20 21:00:00\');
+-----------------------------------------------+
| TIMESTAMPADD(MINUTE,60,\'2019-07-20 21:00:00\') |
+-----------------------------------------------+
| 2019-07-20 22:00:00 |
+-----------------------------------------------+
1 row in set
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