create table tmp1 (id number(11,0),
                   num1 number(11,0),  
                   txt varchar2(10)
                  );
/
insert into tmp1 (id,num1,txt) values(1,10,'test10');
/
insert into tmp1 (id,num1,txt) values(2,2,'test10');
/
insert into tmp1 (id,num1,txt) values(3,4,'test4');
/
create table tmp2 (id number(11,0),
                   num1 number(11,0),  
                   txt varchar2(10)
                  );
insert into tmp2 (id,num1,txt) values(1,10,'test10');
/
insert into tmp2 (id,num1,txt) values(2,2,'test10');
/
create table tmp3 (id number(11,0),
                   num1 number(11,0),  
                   txt varchar2(10)
                  );
insert into tmp3 (id,num1,txt) values(1,5,'test10');
/
insert into tmp3 (id,num1,txt) values(2,2,'test10');

select
  tmp1.num1,
  tmp2.num1,
  tmp3.num1,
  CASE 
      WHEN tmp1.num1 is not null AND tmp2.num1 is not null AND tmp3.num1 is not null then 3
      WHEN tmp1.num1 is not null AND tmp2.num1 is null AND tmp3.num1 is null then 2
      WHEN tmp1.num1 is not null AND tmp2.num1 is not null AND tmp3.num1 is null then 1
  end as cnt
from 
  tmp1
      left join tmp2 on tmp1.num1=tmp2.num1
      left join tmp3 on tmp1.num1=tmp3.num1
/

select
  tmp1.num1,
  tmp2.num1,
  tmp3.num1,
  (select SUM(cnt) 
                  from (
                          select 1 as cnt from 
                          dual
                          where 1=case when tmp1.num1 is not null then 1 end
                          union all
                          select 1 from 
                          dual
                          where 1=case when tmp2.num1 is not null then 1 end
                          union all
                          select 1 from 
                          dual
                          where 1=case when tmp2.num1 is not null then 1 end
                        )
  ) as cnt
from 
  tmp1
      left join tmp2 on tmp1.num1=tmp2.num1
      left join tmp3 on tmp1.num1=tmp3.num1