MySQL datediff 奇怪的结果

Question

datediff 函数的结果很奇怪。对于不同和相同的时间戳为零？

select datediff('2015-04-25 20:37:45','2015-04-25 05:20:00');
+-------------------------------------------------------+
| datediff('2015-04-25 20:37:45','2015-04-25 05:20:00') |
+-------------------------------------------------------+
|                                                     0 |
+-------------------------------------------------------+

select datediff('2015-04-25 20:37:45','2015-04-25 20:37:45');
+-------------------------------------------------------+
| datediff('2015-04-25 20:37:45','2015-04-25 20:37:45') |
+-------------------------------------------------------+
|                                                     0 |
+-------------------------------------------------------+

Answer 1

如果您查看 MySQL 手册：

DATEDIFF
DATEDIFF() returns expr1 − expr2 expressed as a value in days from one date to the other. expr1 and expr2 are date or date-and-time expressions. Only the date parts of the values are used in the calculation

所以你得到的是正确的。

如果您正在寻找时差，我建议您查看 TIMEDIFF or TIMESTAMPDIFF。

如果您想得到分钟数的差异，最好的方法是TIMESTAMPDIFF。

这里有一个你如何做的例子：

SELECT TIMESTAMPDIFF(MINUTE, '2015-04-25 20:37:45','2015-04-25 05:20:00');
+--------------------------------------------------------------------+
| TIMESTAMPDIFF(MINUTE, '2015-04-25 20:37:45','2015-04-25 05:20:00') |
+--------------------------------------------------------------------+
|                                                               -917 |
+--------------------------------------------------------------------+

Answer 2

datediff 将对日期进行计算并找出天数差异，但是您可以使用 timestampdiff 来表示不同的差异，例如 hour、min 等

mysql> select timestampdiff(hour,'2015-04-25 05:20:00','2015-04-25 20:37:45') as hour;
+------+
| hour |
+------+
|   15 |
+------+
1 row in set (0.00 sec)

Answer 3

如果你想比较两个时间戳的差异小于一天，你应该使用 TIMEDIFF() 函数而不是 DATEDIFF。例如：

select TIMEDIFF('2015-04-25 20:37:45','2015-04-25 05:20:00');

或秒内的结果：

select TIME_TO_SEC(TIMEDIFF('2015-04-25 20:37:45','2015-04-25 05:20:00'));

更多详情：

MySQL: how to get the difference between two timestamps in seconds

希望这对您有所帮助:)

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