Question

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

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 

Edit: I was hoping for a solution that would not require changes when Congress adjusts DST laws, as they did in 2007. The posted solutions will work, though.

Answer 1

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; 

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.