And V2 is even better

CREATE FUNCTION [dbo].[HiLoDate2]

(

@date1 datetime,

@date2 datetime,

@date3 datetime,

@date4 datetime

)

RETURNS TABLE

AS

RETURN

(

with cte (max1,max2, min1,min2 ) as

(select case when @date1 >= @date2 then @date1 else @date2 end

,case when @date3 >= @date4 then @date3 else @date4 end

,case when @date1 <= @date2 then @date1 else @date2 end

,case when @date3 <= @date4 then @date3 else @date4 end

)

select case when min1 <= min2 then min1 else min2 end as LoDate

,case when max1 >= max2 then max1 else max2 end as HiDate

from cte

)

GO

/* TEST -- compare executions plans

select *

from dbo.HiLoDate('3/1/2012','3/15/2011','2/1/2012','11/1/2011')

select *

from dbo.HiLoDate2('3/1/2012','3/15/2011','2/1/2012','11/1/2011')

*/