T-SQL - Find differences for PK's in a single table (self join?)

Question

My situation is this. I have a table of products with a pk "Parent" which has "Components" The data looks something like this

Parent(PK)    Component
Car1          Wheel
Car1          Tyre
Car1          Roof
Car2          Alloy
Car2          Tyre 
Car2          Roof
Car3          Alloy
Car3          Tyre
Car3          Roof 
Car3          Leather Seats

Now what I want to do is some query that I can feed two codes in and see the differences... IE If I feed in "Car1", "Car2" it would return something like;

Parent       Component
Car1         Wheel
Car2         Alloy

As this is the difference between the two. If I said "Car1", "Car3" I would expect;

Parent       Component
Car1         Wheel
Car3         Alloy
Car3         Leather Seats

Your help with this matter would be greatly appreciated.

Answer 1

Without GROUP BY or UNION:

create table Products (
    Parent varchar(20) not null,
    Component varchar(20) not null
)
insert into Products (Parent,Component)
select 'Car1','Wheel' union all
select 'Car1','Tyre' union all
select 'Car1','Roof' union all
select 'Car2','Alloy' union all
select 'Car2','Tyre' union all
select 'Car2','Roof' union all
select 'Car3','Alloy' union all
select 'Car3','Tyre' union all
select 'Car3','Roof' union all
select 'Car3','Leather Seats'
go
select
    ISNULL (a.Parent,b.Parent) as Parent,
    ISNULL (a.Component,b.Component) as Component
from
    Products a
        full outer join
    Products b
        on
            a.Component = b.Component and
            a.Parent = 'Car1' and
            b.Parent = 'Car3'
where
    (a.Parent = 'Car1' and b.Parent is null) or
    (b.Parent = 'Car3' and a.Parent is null)