I'm having some bother with variables?

> In ms sql if @aS @aF is NULL then @a is always null

Yes. Take a look MS SQL's ISNULL(..) function. You can use it to substitute a default value whenever the main value is null. Use whatever default value is appropriate in your case.

set @a = ISNULL(@amountSpot, 0) + ISNULL(@amountForward , 0)

nikos101 wrote:
> I'm having some bother with variables?
>
> In ms sql if @aS @aF is NULL then @a is always null.
>
> @a = @aS + @aF
>
> What is the best way to make sure @a contains a value if either @amountSpot
> or @amountForward contains a number?
>
> set @a = @amountSpot + @amountForward
>

You need one of the NULL functions, probably COALESCE(), but pick for
yourself.
http://www.w3schools.com/SQL/sql_isnull.asp
SQL NULL Functions