try this:
Declare @D Datetime
Set @D = [Some date for which you want the following months' first sunday]
Select DateAdd(day, (8-DatePart(weekday,
DateAdd(Month, 1+DateDiff(Month, 0, @D), 0)))%7,
DateAdd(Month, 1+DateDiff(Month, 0, @D), 0))
EDIT Notes:
The first of next Month is given by the expression:
DateAdd(Month, 1+DateDiff(Month, 0, @D), 0)
or by:
which can be modified to give the first of the month two months from now by changing the 1 to a 2:
DateAdd(Month, 2+DateDiff(Month, 0, @D), 0)
EDIT: In response to @NissanFan, and @Anthony: to modify this to return the first Monday Tuesday Wednesday, etc, change the value 8 to a 9, 10, 11, etc....
Declare @Sun TinyInt Set @Sun = 8
Declare @Mon TinyInt Set @Mon = 9
Declare @Tue TinyInt Set @Tue = 10
Declare @Wed TinyInt Set @Wed = 11
Declare @Thu TinyInt Set @Thu = 12
Declare @Fri TinyInt Set @Fri = 13
Declare @Sat TinyInt Set @Sat = 14
Declare @D Datetime, @FONM DateTime -- FirstofNextMonth
Set @D = [Some date for which you want the following months' first sunday]
Set @FONM = DateAdd(Month, 1+DateDiff(Month, 0, @D),0)
Select
DateAdd(day, (@Sun -DatePart(weekday, @FONM))%7, @FONM) firstSunInNextMonth,
DateAdd(day, (@Mon -DatePart(weekday, @FONM))%7, @FONM) firstMonInNextMonth,
DateAdd(day, (@Tue -DatePart(weekday, @FONM))%7, @FONM) firstTueInNextMonth,
DateAdd(day, (@Wed -DatePart(weekday, @FONM))%7, @FONM) firstWedInNextMonth,
DateAdd(day, (@Thu -DatePart(weekday, @FONM))%7, @FONM) firstThuInNextMonth,
DateAdd(day, (@Fri -DatePart(weekday, @FONM))%7, @FONM) firstFriInNextMonth,
DateAdd(day, (@Sat -DatePart(weekday, @FONM))%7, @FONM) firstSatInNextMonth