众所周知，DATEDIFF() 函数用于获取两个日期之间的天数差。因此，它也很可能返回负值。
mysql> select * from differ; +------------+-------------+ | OrderDate | WorkingDate | +------------+-------------+ | 2017-10-22 | 2017-10-29 | | 2017-10-25 | 2017-10-30 | | 2017-10-25 | 2017-11-30 | +------------+-------------+ 3 rows in set (0.00 sec)
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以上查询将返回表“differ”中的值。现在，如果有人想要获取 OrderDate 和workingDate 之间的差异，那么输出将为负数，如下所示 -
mysql> Select DATEDIFF(OrderDate, WorkingDate)AS 'DIFFERENCE IN DAYS' from differ; +--------------------+ | DIFFERENCE IN DAYS | +--------------------+ | -7 | | -5 | | -36 | +--------------------+ 3 rows in set (0.00 sec)
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但是我们可以使用 MySQL ABS() 函数来忽略这些负值，具体操作如下 -
mysql> Select ABS(DATEDIFF(OrderDate, WorkingDate))AS 'DIFFERENCE IN DAYS' from differ; +--------------------+ | DIFFERENCE IN DAYS | +--------------------+ | 7 | | 5 | | 36 | +--------------------+ 3 rows in set (0.00 sec)
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