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

Question

I am trying to achieve something like the below in WHERE clause in sql.

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

I tried the following:

WHERE ((@zipCode IS NOT NULL AND ([Portal].[dbo].[Address].PostalCode=@zipCode)) OR (@zipCode IS NULL AND ([Portal].[dbo].[Address].Position.Filter(@radiusBuff) = 1)))

which is wrong. Can anyone help in framing the exact statement. Thanks!

Answer 1

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