SQL - Number of minutes in a month given month number - sql-server

Question

I have a MS SQL table which contains a column containing month numbers (stored as an int).
I would like to get the number of minutes in the month using the month number.
After looking through Stack Overflow I came across the following code which I thought I could adapt to tell me the number of minutes by replacing the word DAY with MINUTE but to no avail.
DECLARE #ADate DATETIME
SET #ADate = GETDATE()
SELECT DAY(EOMONTH(#ADate)) AS DaysInMonth
The month is a 1 or 2 digit int depending on the month.
UPDATE:
I do have the year as well stored in another column.

Answer 1

Use DATEDIFF with MINUTE.
IF OBJECT_ID('tempdb..#Month') IS NOT NULL
DROP TABLE #Month
CREATE TABLE #Month (
MonthNumber INT,
Year INT)
INSERT INTO #Month (
MonthNumber,
Year)
VALUES
(1, 2018),
(2, 2018),
(2, 2016), -- Leap
(12, 2018)
SELECT
M.MonthNumber,
M.Year,
FirstDay = DATEFROMPARTS(M.Year, M.MonthNumber, 1),
FirstDayNextMonth = DATEADD(
MONTH,
1,
DATEFROMPARTS(M.Year, M.MonthNumber, 1)),
Minutes = DATEDIFF(
MINUTE,
DATEFROMPARTS(M.Year, M.MonthNumber, 1), -- FirstDay
DATEADD(MONTH, 1, DATEFROMPARTS(M.Year, M.MonthNumber, 1))) -- FirstDayNextMonth
FROM
#Month AS M
Results:
MonthNumber Year FirstDay FirstDayNextMonth Minutes
1 2018 2018-01-01 2018-02-01 44640
2 2018 2018-02-01 2018-03-01 40320
2 2016 2016-02-01 2016-03-01 41760
12 2018 2018-12-01 2019-01-01 44640

Answer 2

That's a deceptively tricky question. It's not only that the number of days in February changes in leap years. The number of hours in a date changes during the transition to Summer/Winter time. To calculate the correct difference in minutes between two dates you need to know the correct time offset as well.
Instead of looking up the offset for each date though, you can use the timezone. The timezone information contains all the rules needed to calculate the time offset for past and future dates, provided the OS's timezone information is kept up to date.
SQL Server 2016 and later support timezones with the AT TIME ZONE expression :
For example these queries:
select datetimefromparts(2018,3,25,0,0,0,0) at TIME ZONE 'E. Europe Standard Time'
select datetimefromparts(2018,3,26,0,0,0,0) at TIME ZONE 'E. Europe Standard Time'
Return
2018-03-25 00:00:00.000 +02:00
2018-03-26 00:00:00.000 +03:00
March 25 had 23 hours instead of 24. The difference of the two days in minutes is 1380 instead of the usual 1440:
select datediff(mi,
datetimefromparts(2018,3,25,0,0,0,0) at TIME ZONE 'E. Europe Standard Time',
datetimefromparts(2018,3,26,0,0,0,0) at TIME ZONE 'E. Europe Standard Time')
-----
1380
You can pass the timezone name as a parameter :
declare #mytimezone nvarchar(40)='E. Europe Standard Time'
select datetimefromparts(2018,3,25,0,0,0,0) at TIME ZONE #mytimezone
select datetimefromparts(2018,3,26,0,0,0,0) at TIME ZONE #mytimezone
To calculate the correct number of minutes in a month, you could use the difference in minutes between the current and the next month's 1st day on a specific timezone with AT TIME ZONE. This would ensure the correct offsets are used.
A query that calculates the difference in minutes correctly could look like this :
declare #mytimezone nvarchar(40)='E. Europe Standard Time'
select year,month,
datediff(mi,
datetimefromparts(M.Year,M.Month,1,0,0,0,0) at TIME ZONE #mytimezone,
dateadd(MONTH,1,datetimefromparts(M.Year,M.Month,1,0,0,0,0)) at TIME ZONE #mytimezone
)
from (values
(2016,2),
(2018,1),
(2018,2),
(2018,3),
(2018,4),
(2018,5),
(2018,6),
(2018,7),
(2018,8),
(2018,9),
(2018,10),
(2018,11),
(2018,12) ) M(Year,Month)
You can create a function to calculate the minutes. Either a scalar function that can be used in the SELECT clause :
CREATE FUNCTION MinutesInMonth
(
#Year INT,
#Month INT,
#timezone nvarchar(40)
)
RETURNS INT
AS
BEGIN
Return
datediff(mi,
datetimefromparts(#year,#month,1,0,0,0,0) at TIME ZONE #timezone,
dateadd(MONTH,1,datetimefromparts(#year,#month,1,0,0,0,0)) at TIME ZONE #timezone
)
END
...
select year,month,dbo.MinutesInMonth(year,month,#mytimezone)
from (values
(2018,10),
(2018,11),
(2018,12)
) M(Year,Month)
Or an inline table function that can be used in the FROM clause and gets inlined in the query itself :
CREATE FUNCTION MinutesInMonth
(
#Year INT,
#Month INT,
#timezone nvarchar(40)
)
RETURNS TABLE
RETURN (select datediff(mi,
datetimefromparts(#year,#month,1,0,0,0,0) at TIME ZONE #timezone,
dateadd(MONTH,1,datetimefromparts(#year,#month,1,0,0,0,0))
At TIME ZONE #timezone) as Minutes
)
select year,month,Minutes
from (values
(2016,2),
(2018,1),
(2018,2),
(2018,3),
(2018,4),
(2018,5),
(2018,6),
(2018,7),
(2018,8),
(2018,9),
(2018,10),
(2018,11),
(2018,12)
) M(Year,Month)
cross apply dbo.MinutesInMonth(year,month,#mytimezone)

Answer 3

Try this out :-
DECLARE #Year INT = 2016, #Month INT = 2;
DECLARE #Date DATE = DATETIMEFROMPARTS(#Year,#Month, 1, 0, 0, 0, 0) AT TIME ZONE 'Sri Lanka Standard Time';
SELECT DAY(EOMONTH(#Date)) * 24 * 60;
Alternatively you can create a scalar function as follows:-
CREATE FUNCTION GetMinutesOfMonth
(
#Year INT,
#Month INT,
#TimeZone VARCHAR(50) = NULL
)
RETURNS INT
AS
BEGIN
DECLARE #MinutesOfMonth INT, #CurrentTimeZone VARCHAR(50);
EXEC MASTER.dbo.xp_regread 'HKEY_LOCAL_MACHINE',
'SYSTEM\CurrentControlSet\Control\TimeZoneInformation',
'TimeZoneKeyName',#CurrentTimeZone OUT;
SET #TimeZone = ISNULL((SELECT [name] FROM SYS.time_zone_info WHERE [name] = #TimeZone), #CurrentTimeZone)
DECLARE #Date DATE = DATETIMEFROMPARTS(#Year, #Month, 1, 0, 0, 0, 0) AT TIME ZONE #TimeZone;
SELECT #MinutesOfMonth = DAY(EOMONTH(#Date)) * 24 * 60;
RETURN #MinutesOfMonth;
END
GO
and use it as:-
DECLARE #Year INT = 2016, #Month INT = 2;
SELECT dbo.GetMinutesOfMonth(#Year, #Month, 'Sri Lanka Standard Time');
If the timezone of the current machine is same as the dates being considered, you may use the function as follows:-
DECLARE #Year INT = 2016, #Month INT = 2;
SELECT dbo.GetMinutesOfMonth(#Year, #Month, DEFAULT);