SQL Server 2008 R2 - convert all datetime parts (as ints) into a datetime column - tsql

Question

I have a table that has the datetime pieces (year, month, day, hour, minute, second, millisecond) stored as integers. I'd like to concatenate them into a single datetime column.
I've tried various approaches but none work - there seems to be no simple way to put these items together?

Answer 1

You can convert each part to a varchar and concatenate them together in the format of an ISO datetime string. Then use Convert to convert the string to a DateTime.
Here is an example. You would need to replace each hard coded integer with the name of the column from your table.
SELECT CONVERT(DATETIME, CAST(2016 AS VARCHAR(4)) -- year
+ '-' + CAST('0' + CAST(8 AS VARCHAR(2)) AS VARCHAR(2)) -- month
+ '-' + RIGHT('0' + CAST(13 AS VARCHAR(2)), 2) -- day of month
+ 'T' + RIGHT('0' + CAST(16 AS VARCHAR(2)), 2) -- hours (I assume its military time (24 hours))
+ ':' + RIGHT('0' + CAST(32 AS VARCHAR(2)), 2) -- minutes
+ ':' + RIGHT('0' + CAST(07 AS VARCHAR(2)), 2) -- seconds
+ '.' + RIGHT('000' + CAST(64 AS VARCHAR(3)), 3)) AS MyDate -- milliseconds
FROM yourTable
Or with column names (assumed)
SELECT CONVERT(DATETIME, CAST(yt.Year AS VARCHAR(4)) -- year
+ '-' + CAST('0' + CAST(yt.Month AS VARCHAR(2)) AS VARCHAR(2)) -- month
+ '-' + RIGHT('0' + CAST(yt.Day AS VARCHAR(2)), 2) -- day of month
+ 'T' + RIGHT('0' + CAST(yt.Hours AS VARCHAR(2)), 2) -- hours (I assume its military time (24 hours))
+ ':' + RIGHT('0' + CAST(yt.Minutes AS VARCHAR(2)), 2) -- minutes
+ ':' + RIGHT('0' + CAST(yt.Seconds AS VARCHAR(2)), 2) -- seconds
+ '.' + RIGHT('000' + CAST(yt.Milliseconds AS VARCHAR(3)), 3)) AS MyDate -- milliseconds
FROM yourTable yt
One more note. Microsoft recommends that you use DateTime2 instead of DateTime to persist date time values starting with Sql Server 2008 (which you tagged in your question).

Answer 2

Prior to sql server 2012, you can use a series of nested DATEADD() functions to mimic DATETIMEFROMPARTS() function
Create and populate sample data (In your next question, please save us this step)
DECLARE #T as table
(
cYear int,
cMonth int,
cDay int,
cHour int,
cMinute int,
cSecond int,
cMillisecond int
)
INSERT INTO #T VALUES(2016, 6, 22, 16, 34, 25, 3)
The query:
SELECT *,
DATEADD(MILLISECOND, cMillisecond,
DATEADD(SECOND, cSecond,
DATEADD(MINUTE, cMinute,
DATEADD(HOUR, cHour,
DATEADD(DAY, cDay -1,
DATEADD(MONTH, cMonth - 1,
DATEADD(YEAR, cYear - 2000, '2000-01-01')
)
)
)
)
)
) As TheDate
FROM #T
Results:
cYear cMonth cDay cHour cMinute cSecond cMillisecond TheDate
----- ------ ---- ----- ------- ------- ------------- -----------------------
2016 6 22 16 34 25 3 2016-06-22 16:34:25.003
Note that the base date I'm using is January 1st 2000, therefor you need to subtract 2000 from the year, 1 from the month and 1 from the days.