XOR Function - SQL Server

The following SQL statement demonstrates a technique for calcuating an XOR value.

declare 
     @a bit
    ,@b bit

select
     @a = 0
    ,@b = -1

select result = 'Exactly one is null? ' + 
    case coalesce(abs(sign(@a)),-1) * coalesce(abs(sign(@b)),-1) 
    when -1 then 'TRUE' 
    else 'FALSE' 
    end