Help with SQL query

Hello Experts,

I would very much appreciate some expert advise / help on a query I am writing, below is an example of what I am writing. I have a user interface that will present to the users several teat boxes / search form, The ID, month and year always have a default value but they have the option of entering an account # , PO # and a date range, if they leave the date range, Account and Account blank then it will return result for just ID, month, year ( default values).. What is the best way to implement the query so I don't have to repeat the select statement for the Date Range section, and is this the best way to implement this type of search interfaces in my SQL.

SO basically, the user will have the option of searching for specific record or leaving the parameters blank which will return all records..

Any help will be greatly appreciated... Thank You..

     @Year     AS SMALLINT = NULL,
@month     AS SMALLINT = NULL,
@Acct_Mask  as VARCHAR(20) = NULL
@PO_Num     AS VARCHAR(20) = NULL
@StartDate      AS Datetime = NULL,
@EndDate        AS Datetime = NULL,

IF @StartDate IS NULL OR @StartDate = '' OR @EndDate IS NULL OR @EndDate = ''

SELECT * from Table1
  ID = @ID
  AND month= @month
  AND  Year = @Year
  AND (ISNULL(@Acct_Mask, '') = '' OR (Account  LIKE @Acct_Mask))
  AND (ISNULL(@PO_Num , '') = '' OR (Po = @PO_Num ))

SELECT * from Table1
ID = @ID
AND month= @month
AND Year = @Year
AND (ISNULL(@Acct_Mask, '') = '' OR (Account LIKE @Acct_Mask))
AND (ISNULL(@PO_Num , '') = '' OR (Po = @PO_Num ))

 AND CheckDate >= @StartDate AND CheckDate <= @EndDate


Perhaps something like:

select *
  from table1
 where id=@id
   and [month]=@month
   and [year]=@year
   and (isnull(@acct_mask,'')=''
    or  account like @acct_mask
   and (isnull(@po_num,'')=''
    or  po like @po_num
   and checkdate>=isnull(@startdate,cast('1800-01-01 00:00:00.000' as datetime))
   and checkdate<dateadd(day,1,isnull(@enddate,cast('9999-12-30 23:59:59.998' as datetime)))

Thank you, really appreciate your help..