To pass a optional parameters to a stored procedure in SQL Server, declare the parameter with the default value.

Create Procedure proc_Test

@a int,

@b int =5 -- Provided with the default value.

as

begin

       Select @a, @b

end

Note:

When using optional parameters at first, specify it with the parameter name during execution

For example, if @a is an optional parameter, to execute this stored proecedure, specify it as follows 

EXEC proc_Test @b=3