sql：mysql：函数：TIMESTAMPDIFF函数实现TimeStamp字段相减，求得时间差

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 函数内指定是minute，则最终结果value值的单位是分钟，如果函数内指定为hours，则最终结果value值单位为小时。

//UPLOAD_TIME 减去 CREATE_DTTM 求得时间差，以分钟数计时
select avg(TIMESTAMPDIFF(MINUTE,CREATE_DTTM,UPLOAD_TIME)) value,LEFT(CREATE_DTTM,10) time from 表名
WHERE
    CREATE_DTTM >= '2018-01-21'
AND CREATE_DTTM <=DATE_ADD( '2019-02-19',INTERVAL 1 DAY) and UPLOAD_TIME is not null
group by LEFT(CREATE_DTTM,10)

参考：https://blog.csdn.net/yiifaa/article/details/78611079

https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_microsecond

mysql> SELECT TIMESTAMPDIFF(MONTH,'2003-02-01','2003-05-01');
        -> 3
mysql> SELECT TIMESTAMPDIFF(YEAR,'2002-05-01','2001-01-01');
        -> -1
mysql> SELECT TIMESTAMPDIFF(MINUTE,'2003-02-01','2003-05-01 12:05:55');
        -> 128885