declare @sample table (id int, [type] char(1))

insert @sample select 1,'A' 
insert @sample select 1,'B'
insert @sample select 2,'A'
insert @sample select 3,'B'
insert @sample select 4,'D'

select s1.id, 'A' as missingType
from @sample s1
left join @sample sA on sA.id = s1.id and sA.[type] = 'A'
where sA.id is null 
union
select s1.id, 'B' as missingType
from @sample s1
left join @sample sB on sB.id = s1.id and sB.[type] = 'B'
where sB.id is null

declare @sample table (id int, [type] char(1));

insert @sample select 1,'A' ;
insert @sample select 1,'B';
insert @sample select 2,'A';
insert @sample select 3,'B';
insert @sample select 4,'D';

with ReqIdsTypes as (
select distinct
    id,
    dt.[type]
from
    @sample
    cross join (select [type] from (values ('A'),('B'))dt([type]))dt([type]))
select id as MissingId, [type] as MissingType from ReqIdsTypes
except
select id, [type] from @sample;