在Oracle中，如何检测夏令时的开始/结束日期? [英] In Oracle, how can I detect the date on which daylight savings time begins / ends?

问题描述

Oracle中是否有一种方法可以为我的语言环境选择夏令时的转换日期?

Is there a way in Oracle to select the date on which daylight savings will switch over for my locale?

大概相当于这样的东西会很好:

Something vaguely equivalent to this would be nice:

SELECT CHANGEOVER_DATE
FROM SOME_SYSTEM_TABLE
WHERE DATE_TYPE = 'DAYLIGHT_SAVINGS_CHANGEOVER'
  AND TO_CHAR(CHANGEOVER_DATE,'YYYY') = TO_CHAR(SYSDATE,'YYYY');  -- in the current year

我希望能像2007年那样在国会调整DST法律时不需要任何更改的解决方案.不过，发布的解决方案仍然可以使用.

推荐答案

我们使用以下两个函数来计算任何给定年份(美国，2007年之后)的开始和结束日期.

We use the following two functions to calculate the start and end dates for any given year (post 2007, US).

Function DaylightSavingTimeStart (p_Date IN Date)
Return Date Is
   v_Date       Date;
   v_LoopIndex  Integer;
Begin
   --Set the date to the 8th day of March which will effectively skip the first Sunday.
   v_Date := to_date('03/08/' || to_char(p_Date,'YYYY') || '02:00:00 AM','MM/DD/YYYY HH:MI:SS PM');
   --Advance to the second Sunday.
   FOR v_LoopIndex IN 0..6 LOOP
      If (RTRIM(to_char(v_Date + v_LoopIndex,'DAY')) = 'SUNDAY') Then
         Return v_Date + v_LoopIndex;
      End If;
   END LOOP;
End;

Function DaylightSavingTimeEnd (p_Date IN Date)
Return Date Is
   v_Date       Date;
   v_LoopIndex  Integer;
Begin
   --Set Date to the first of November this year
   v_Date := to_date('11/01/' || to_char(p_Date,'YYYY') || '02:00:00 AM','MM/DD/YYYY HH:MI:SS PM');
   --Advance to the first Sunday
   FOR v_LoopIndex IN 0..6 LOOP
      If (RTRIM(to_char(v_Date + v_LoopIndex,'DAY')) = 'SUNDAY') Then
         Return v_Date + v_LoopIndex;
      End If;
   END LOOP;
End;

可能有一种更简单的方法，但是这些方法对我们有用.当然，此查询不知道您所在的位置是否遵守夏令时.为此，您需要位置数据.

There is probably a simpler way to do it, but these have worked for us. Of course this query doesn't know whether daylight saving time is observed for where you are. For that you will need location data.

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