Detect if a date is in Daylight saving time in MySql

Question

I have inherited a legacy application where all the dates and times are stored in the local timezone (UK). I am not in a position to change how these are stored.

Howeve

Answer 1

As an alternative, here are some functions to determine whether the North American Daylight Savings rules are in effect.

As of 2007* the rule in North America has been that Daylight Savings (DST):

• starts at 2am (local time) on the 2nd Sunday of March
• ends at 2am (local time) on the 1st Sunday of November

*_{(From 1987 to 2006 it was the April's 1st Sunday to October's last Sunday.)}

---

MySQL Functions:

DELIMITER // CREATE FUNCTION DSTstart(dt DATETIME) RETURNS DATETIME DETERMINISTIC BEGIN 
RETURN cast(concat(year(now()),'-3-',(14-WEEKDAY(concat(year(now()),'-3-1'))),' 2:00') as datetime);
END// DELIMITER ;

DELIMITER // CREATE FUNCTION DSTstop(dt DATETIME) RETURNS DATETIME DETERMINISTIC BEGIN 
RETURN cast(concat(year(now()),'-11-',(7-WEEKDAY(concat(year(now()),'-11-1'))),' 2:00') as datetime);
END// DELIMITER ;

DELIMITER // CREATE FUNCTION isDST(dt DATETIME) RETURNS BIT DETERMINISTIC BEGIN 
RETURN (dt>=cast(concat(year(now()),'-3-',(14-WEEKDAY(concat(year(now()),'-3-1'))),' 2:00') as datetime))
AND (dt

---

Just for reference I'll include the VBA and Excel Worksheet versions of the functions:

Excel/Access/etc VBA Functions:

Function DSTstart(dt As Date) As Date 
  DSTstart = CDate(Year(dt) & "-3-" & (15 - Weekday(CDate(Year(dt) & "-3-1"), 2)) & " 2:00")
End Function

Function DSTstop(dt As Date) As Date 
  DSTstop = CDate(Year(dt) & "-11-" & (8 - Weekday(CDate(Year(dt) & "-11-1"), 2)) & " 2:00")
End Function

Function isDST(dt As Date) As Boolean
  isDST = (dt >= CDate(Year(dt) & "-3-" & (15 - Weekday(CDate(Year(dt) & "-3-1"), 2)) & " 2:00") _
          And dt < CDate(Year(dt) & "-11-" & (8 - Weekday(CDate(Year(dt) & "-11-1"), 2)) & " 2:00"))
End Function

---

Excel Worksheet Functions:

DST Start: (returns the date/time that DST begins in the year of the date in [A1])

=DATE(YEAR(A1),3,15-WEEKDAY(DATE(YEAR(A1),3,1),2))+TIMEVALUE("2:00")

DST End: (returns the date/time that DST begins in the year of the date in [A1])

=DATE(YEAR(A1),11,8-WEEKDAY(DATE(YEAR(A1),11,1),2))+TIMEVALUE("2:00")

Is DST?: (returns TRUE if DST is in effect for the date in [A1])

=AND(A1>=DATE(YEAR(A1),3,15-WEEKDAY(DATE(YEAR(A1),3,1),2))+TIMEVALUE("2:00"),A1