Вид
create table t (
A varchar(2) not null,
B varchar(2),
C varchar(2),
D varchar(2)
);
insert t(A,B,C,D)
values
('X','Y',null,null)
,('Y',null,'Z','W')
,('R',null,'T',null)
,('S',null,null,'P');
select t1.A, t1.B, t2.C, t2.D
from t t1
join t t2 on t1.B = t2.A
and coalesce (t2.C, t2.D) is not null;