Difference Between Two Dates Stored Procedure SQL

Hi

I am trying to do my first stored procedure in SQL Server Management 2005 Express. I basically want to take two dates from a table of batch numbers and calculate the time span between the two dates. (The dates will be the first and last datetime that the batch number was recorded in table).

I have my code so far, but it does not compile - throwing incorrect syntax error on the line:

set @firstdate = SELECT top 1 datetimecol from Test_01.Table_1 where batchcol = @batchnumber order by datetimecol ASC

Even then I am not sure I am going the correct route. any hints / opinions would be appreciated.

Cheers

Neil Whitley

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:		<Author,,Name>
-- Create date: <Create Date,,>
-- Description:	<Description,,>
-- =============================================
CREATE PROCEDURE TimeDifferenceSecs 
	-- Add the parameters for the stored procedure here
	@batchnumber int = 99, 
	@vessel varchar(50) = "??",
	@firstdate as datetime,
	@lastdate as datetime,
	@difference as datetime
AS
BEGIN
	-- SET NOCOUNT ON added to prevent extra result sets from
	-- interfering with SELECT statements.
	SET NOCOUNT ON;
 
    -- Insert statements for procedure here
	set @firstdate = SELECT top 1 datetimecol from Test_01.Table_1 where batchcol = @batchnumber order by datetimecol ASC
 
	set @lastdate = SELECT top 1 datetimecol from Test_01.Table_1 where batchcol = @batchnumber order by datetimecol DES
 
	set @difference = Datediff("s",@firstdate,@lastdate)
 
END
GO

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