with
c as
(
  select 0 c from dual where 0=1
  union all select 1 from dual
  union all select 2 from dual
  union all select 3 from dual
)
, t as
(
  select 0 t, 0 g, 0 demo from dual where 0=1
  union all select 1, 1, 1 from dual
  union all select 2, 1, null from dual
  union all select 3, 2, null from dual
)
, s as
(
  select 0 s, 0 c, 0 t from dual where 0=1
  union all select 11, 1, 1 from dual
  union all select 12, 1, 2 from dual
  union all select 21, 2, 1 from dual
  union all select 31, 3, 2 from dual
  union all select 32, 3, 3 from dual
)
, s1 as (select * from s join t using (t) where g = 1 and demo=1)
, s2 as (select * from s join t using (t) where g = 1)
select c.c, s2.s, s2.t, s2.g
from c
left join s1 on (s1.c = c.c)
join s2 on (s2.c = c.c and s2.s != nvl(s1.s,0))
order by c, s