I created a function that will return 2 dates that depend on an input parameter.

When the parameter is:

• 1 - return start date of current week and end date of current week
• 2 - return start date of last week and end date of last week
• 3 - return start date of current month and end date of current month
• 4 - return start date of last month and end date of last month

Could you please suggest improvements? And what name would be more appropriate for this function?

CREATE FUNCTION [ufn_GetRangeOfDates] 
( @Type int
)
RETURNS @Result TABLE     
( StartDate date
, EndDate date
)
AS
BEGIN

  declare @Today date = GetDate()

  -- current weak
  declare @CurrentWeakStart date = dateadd(day, 1-datepart(dw, @Today), CONVERT(date, @Today))
  declare @CurrentWeakEnd date = dateadd(day, 7-datepart(dw,  @Today), CONVERT(date,  @Today))
  -- last week
  declare @LastWeakStart date = DATEADD(dd, DATEPART(DW,@Today)*-1-6, @Today)
  declare @LastWeakEnd date =DATEADD(dd, DATEPART(DW,@Today)*-1, @Today)
  --current month
  declare @CurrentMonthStart date = DateAdd( day, 1 - Day( @Today ), @Today )
  declare @CurrentMonthEnd Date = DateAdd( day, -1, DateAdd( month, 1, @CurrentMonthStart ) )
  -- last month
  declare @LastMonthStart date = DATEADD(MONTH, DATEDIFF(MONTH, 0, @Today)-1, 0)
  declare @LastMonthEnd date = DATEADD(MONTH, DATEDIFF(MONTH, -1, @Today)-1, -1)
  
  insert into @Result
  select CASE @Type
           WHEN 1 THEN @CurrentWeakStart
           WHEN 2 THEN @LastWeakStart
           WHEN 3 THEN @CurrentMonthStart
           WHEN 4 THEN @LastMonthStart
           ELSE NULL
         END
  ,      CASE @Type
           WHEN 1 THEN @CurrentWeakEnd
           WHEN 2 THEN @LastWeakEnd
           WHEN 3 THEN @CurrentMonthEnd
           WHEN 4 THEN @LastMonthEnd
           ELSE NULL
         END
  RETURN
END -- End of ufn_GetRangeOfDates