Here you go.

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

SET ANSI_NULLS ON

GO

SET QUOTED_IDENTIFIER ON

GO

CREATE FUNCTION dbo.HiLoDate

(

@date1 datetime,

@date2 datetime,

@date3 datetime,

@date4 datetime

)

RETURNS TABLE

AS

RETURN

(

with cte (xDate) as (

select @date1

union all

select @date2

union all

select @date3

union all

select @date4

)

select min(xDate) as LoDate, max(xDate) as HiDate

from

)

GO

/* TEST

select *

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

*/