SQL SERVER: Check if variable is null and then assign statement for Where Clause

Isnull() syntax is built in for this kind of thing.

declare @Int int = null;

declare @Values table ( id int, def varchar(8) )

insert into @Values values (8, 'I am 8');

-- fails
select *
from @Values
where id = @Int

-- works fine
select *
from @Values
where id = isnull(@Int, 8);

For your example keep in mind you can change scope to be yet another where predicate off of a different variable for complex boolean logic. Only caveat is you need to cast it differently if you need to examine for a different data type. So if I add another row but wish to specify int of 8 AND also the reference of text similar to 'repeat' I can do that with a reference again back to the 'isnull' of the first variable yet return an entirely different result data type for a different reference to a different field.

declare @Int int = null;

declare @Values table ( id int, def varchar(16) )

insert into @Values values (8, 'I am 8'), (8, 'I am 8 repeat');

select *
from @Values
where id = isnull(@Int, 8)
and def like isnull(cast(@Int as varchar), '%repeat%')

is null can be used to check whether null data is coming from a query as in following example:

 declare @Mem varchar(20),@flag int
select @mem=MemberClub from [dbo].[UserMaster] where UserID=@uid
if(@Mem is null)
begin
    set @flag= 0;
end
else
begin
    set @flag=1;
end
return @flag;

is null is the syntax I use for such things, when COALESCE is of no help.

Try:

if (@zipCode is null)
  begin
    ([Portal].[dbo].[Address].Position.Filter(@radiusBuff) = 1)   
  end
else 
  begin
    ([Portal].[dbo].[Address].PostalCode=@zipCode )
  end