Define a parameter for searching on days DATEADD / datediff - SQL server 2005

Question

So I have now a grouping of values by their currencies and values, which brings out values for the last 30 days, however I would like to search by date, eventually using a parameter from another table.

;WITH cte AS (SELECT ROW_NUMBER() OVER (ORDER BY date_loaded Asc) AS n, value, 
date_loaded, cast(round(value * 0.0001  / 100 * 0.5 + (value * 0.0001),4)AS dec(12,4)) as buy_rate,
        cast(round(value * 0.0001  / 100 * -0.5 + (value * 0.0001), 4) AS dec(12,4)) as sell_rate 

FROM texchange_rate WHERE source_currency_code = @source_currency_code 
and target_currency_code = @target_currency_code
and date_loaded between dateadd(day, datediff(day, 0 ,getdate())-30, 0) and getdate())

SELECT t2.value, t2.date_loaded, @source_currency_code as source_currency_code,
@target_currency_code as target_currency_code, t2.buy_rate, t2.sell_rate
    FROM cte t2 LEFT JOIN cte t1 ON t2.n = t1.n + 1
    WHERE t2.value <> ISNULL(t1.value, -1)

    order by date_loaded desc

END

I want to define the amount of days that dateadd searches on from a separate table, is this possible? E.g.

from

dateadd(day, datediff(day, 0 ,getdate())-30, 0) and getdate())

to

dateadd(day, datediff(day, 0 ,getdate())@dayparameter, 0) and getdate())

Just to get this working, I've attempted declaring @dayparameter (similar to here - http://msdn.microsoft.com/en-us/library/ms186819%28v=sql.100%29.aspx, although this is for server 2008) at the start of the stored procedure, and placing it inside dateadd gives the error

Msg 102, Level 15, State 1, Procedure proc_getCurrencyHistory, Line 48 Incorrect syntax near '@dayparameter'.

Hope this makes sense.

Answer 1

You still need to perform an operation. If you want to pass in -30 then you need to add, if you want to pass in 30 then you need to subtract.

If @dayparameter is -30:

dateadd(day, datediff(day, 0 ,getdate()) + @dayparameter, 0) and getdate())
-----------------------------------------^ this operator is important

If @dayparameter is 30:

dateadd(day, datediff(day, 0 ,getdate()) - @dayparameter, 0) and getdate())
-----------------------------------------^ this operator is still important