A lot of extra work when it isn't really needed if you ask me.

If OBJECT_ID('tempdb..#Crusty_Table') is not null

Begin

Drop table #Crusty_Table

End

Create table #Crusty_Table (

UniqueIDvarchar(255),

RecordingDatedate

)

Insert Into #Crusty_Table(UniqueID, RecordingDate)

Select '123738','05/21/1969' UNION All

Select '123738','06/09/2010' UNION All

Select '123738','05/29/1967' UNION All

Select '123738','05/29/1967' UNION All

Select '123738','05/31/1967' UNION All

Select '123456','07/09/1977' UNION All

Select '123456','05/29/1967' UNION All

Select '123457','06/09/2010' UNION All

Select '123457','05/21/1969' UNION All

Select '123457','07/09/1977' UNION All

Select '123457','03/07/2007' UNION All

Select '123458','01/15/2014'

Select *

from #Crusty_Table

---------------------------------------------------

---- This is the money shot -----------------------

---------------------------------------------------

select Distinct UniqueID, RecordingDate

--, ROW_NUMBER() over (Partition by UniqueID Order by RecordingDate)

, CASE When (ROW_NUMBER() over (Partition by UniqueID Order by RecordingDate)) = 1 THEN UniqueID

Else UniqueID + '-' + Convert(varchar(255),ROW_NUMBER() over (Partition by UniqueID Order by RecordingDate)-1)

END UniqueID_Alt

From #Crusty_Table

GO

with basedata as (

select

UniqueID,

RecordingDate,

rn = row_number() over (partition by UniqueID order by RecordingDate)

from

#Crusty_Table

)

select

bd.UniqueID,

bd.RecordingDate,

case when bd.rn = 1 then bd.UniqueID else bd.UniqueID + '-' + cast(bd.rn - 1 as varchar) end

from

basedata bd

If OBJECT_ID('tempdb..#Crusty_Table') is not null

Begin

Drop table #Crusty_Table

End

go