Question

I am writing a stored procedure that takes one input argument and can return the related attributes via the optional output parameters. It is defined like this:

CREATE PROCEDURE dbo.sp_get_info
                       @Identifier  nvarchar(50),
                       @Info1       uniqueidentifier = NULL  OUTPUT,
                       @Info2       nvarchar(10) = NULL      OUTPUT,
                       @Info3       int = NULL               OUTPUT

I would like to call the procedure like:

DECLARE @uid uniqueidentifier
...
EXEC sp_get_info @Idenfier = 'a123', 
                 @Info1 = @uid

Getting each output value leads to a different activity. This way, I would like to detect the fact that only the @Info1 output value should be retrieved from elsewhere. This way, the procedure need not to execute possibly costly code that retrieves the other output (now unwanted) arguments.

Firstly, I was thinking about testing like IF @Info1 IS NOT NULL do_something. However, as the OUTPUT says also that the argument can have also the input value (Microsoft SQL) the @uid itself can have the value NULL. This way, the above test does not work.

Is there any technique used to solve the situation?

Thanks, Petr

Answer 1

You could use a @field and @value parameter. The @field could be Info1, Info2, Info3. Now the @value can be null and you still know what field to search.

CREATE PROCEDURE dbo.sp_get_info
    @Identifier nvarchar(50),
    @field nvarchar(50),
    @value nvarchar(50) output

The calling code would have to convert the @value from nvarchar(50) to the required type, but that’s typically easy.