I'm trying to calculate what time a certain time in a time zone is today, so I can schedule something to happen at that time in that time zone.
I've got a table with what I have termed the Nominal Time, which is stored as a
datetimeoffset with an arbitrary date, as the only parts I care about is the time and the time zone offset. So, the Nominal Time column has values along the lines of:
2014-07-01 10:00:00.0000000 +02:00 2014-07-01 10:00:00.0000000 -05:00 2014-07-01 10:00:00.0000000 -07:00 2014-07-01 10:00:00.0000000 +01:00
(In this case 10am is my time I want to schedule this events). From this, I want to get that time today, so these would become:
2014-07-02 10:00:00.0000000 +02:00 2014-07-02 10:00:00.0000000 -05:00 2014-07-02 10:00:00.0000000 -07:00 2014-07-02 10:00:00.0000000 +01:00
when run at the date of this writing (2014-07-02). I currently have SQL that does this, but I don't really like it:
With NominalTimes as (select Id, NominalTime, SYSDATETIMEOFFSET() Now from FaxQueue where status=0), CalcTimes as (select Id, NominalTime, Now, DATEPART(year,Now) NomYear, DATEPART(month,Now) NomMonth,DATEPART(day,Now) NomDay, DATEPART(hour,NominalTime) NomHour,DATEPART(minute,NominalTime) NomMinute, DATEPART(tzoffset,NominalTime) NomOffset from NominalTimes) select Id, NominalTime, Now, DATETIMEOFFSETFROMPARTS(Nomyear,NomMonth,NomDay,NomHour,NomMinute,0,0,NomOffset/60,NomOffset%60,0) from CalcTimes
(Excuse the excessive CTEs; I'm trying to build this up bit by bit.) The end goal of this is to have a query that returns a list of rows where the nominal time happens within the next, say, hour (actual window size isn't important).
I will also note that from the function of the program, I do not need to worry about a time straddling a daylight saving time transition (the program is meant to run before DST happens in a time zone, and deliver a notification).
Is there a better way of doing these date calculations in SQL, or is this really about as good as it's going to get?