Question

I want to create a procedure in SQL Server that will select and join two tables. The parameters @company, @from and @to are always set but @serie_type can be NULL. If @serie_type is not NULL i just want to include the specified types, simple AND S.Type = @serie_type, but if @serie_type is NULL i want to include all types, simple, just dont include the AND statement. My problem is that i dont know if @serie_type will be set therefore i would like o have something like this:

/* pseudocode */
??? = AND (IF @serie_type IS NOT NULL S.Type = @serie_type)

Here is a simpifyed version of procedure:

CREATE PROCEDURE Report_CompanySerie
    @company    INT,
    @serie_type INT,
    @from       DATE,
    @to         DATE
AS
BEGIN
    SELECT
        *
    FROM Company C
        JOIN Series S ON S.Company_FK = C.Id
    WHERE C.Id = @company 
        AND S.Created >= @from
        AND S.Created <= @to
/* HERE IS MY PROBLEM */        
        AND ???
END
GO

Don’t want to duplicate the select becaust the real select is way bigger then this.

Answer 1

There is no need to do AND (@serie_type IS NULL OR S.Type = @serie_type) as SQL Server has a built in function to do this logic for you.

Try this:

   .
   .
   AND  S.Type = isnull( @serie_type, S.Type)

This returns

true if @serie_type is null or the result of @serie_type = S.Type if @serie_type is not null.

From the MSDN:

IsNull Replaces NULL with the specified replacement value.

ISNULL ( check_expression , replacement_value )

The value of check_expression is returned if it is not NULL;
otherwise, replacement_value is returned after it is implicitly
converted to the type of check_expression, if the types are different.