Question

需要帮助您了解如何计算两个日期之间的月份，能够计算日期之间的月份，而不是年份

ID  StartDate   Enddate
1   1/1/2016    4/23/2019
2   1/1/2016    4/30/2017
3   1/1/2016    12/31/2018
4   1/1/2017    4/23/2019
5   5/20/2017   11/30/2017



ID  StartDate   Enddate        2016 2017  2018  2019
1   1/1/2016    4/23/2019        12   12    12     4
2   1/1/2016    4/30/2017        12    4     0     0
3   1/1/2016    12/31/2018       12   12    12     0
4   1/1/2017    4/23/2019         0   12    12     4
5   5/20/2017   11/30/2017        0    7     0     0

Answer 1

在SQL Server中，这样的间隔计数很难。如果数据库支持least()和greatest()，则要简单得多。这是一种冗长的方法：

select id, startdate, enddate,
       (case when startdate >= '2017-01-01' or enddate < '2016-01-01' then 0
             when startdate < '2016-01-01' and enddate >= '2017-01-01' then 12
             when startdate >= '2016-01-01' and enddate >= '2017-01-01' then 13 - month(startdate)
             when startdate < '2016-01-01' then month(enddate)
             else month(enddate) + 1 - month(startdate) 
        end) as months_2016,
       (case when startdate >= '2018-01-01' or enddate < '2017-01-01' then 0
             when startdate < '2017-01-01' and enddate >= '2018-01-01' then 12
             when startdate >= '2017-01-01' and enddate >= '2018-01-01' then 13 - month(startdate)
             when startdate < '2017-01-01' then month(enddate)
             else month(enddate) + 1 - month(startdate) 
        end) as months_2017,
       (case when startdate >= '2019-01-01' or enddate < '2018-01-01' then 0
             when startdate < '2018-01-01' and enddate >= '2019-01-01' then 12
             when startdate >= '2018-01-01' and enddate >= '2019-01-01' then 13 - month(startdate)
             when startdate < '2018-01-01' then month(enddate)
             else month(enddate) + 1 - month(startdate) 
        end) as months_2018
from t;

这基本上处理了不同的条件，即开始日期是在相关年份之前，期间还是之后，而结束日期是相同的。

Answer 2

如果表中有年份，则可以像这样进行动态透视，这样可以省去手动声明列的麻烦：

extension Data {
func toByteArray() -> [UInt8]? {
    var byteData = [UInt8](repeating:0, count: self.count)
    self.copyBytes(to: &byteData, count: self.count)
    return byteData
  }
}

按年份计算两个日期之间的月份

2 个答案: