select student_no,

       case when b.student_no is null '없음' 

        else '보유'

       end as yn

  from 학번테이블 a,  (select distinct student_no from 자격증테이블) b

where a.student_no = b.student_no(+)

WITH 학번 AS (
SELECT '01' 학번 FROM DUAL UNION ALL
SELECT '02' FROM DUAL UNION ALL
SELECT '03' FROM DUAL
),
자격증 AS (
SELECT '01' 학번, '운전면허' 자격증 FROM DUAL UNION ALL
SELECT '01' 학번, '워드' 자격증 FROM DUAL UNION ALL
SELECT '03' 학번, '워드' 자격증 FROM DUAL
)
SELECT A.학번,
       CASE WHEN COUNT(자격증) >= 1 THEN '보유' ELSE  '미보유' END,
       COUNT(자격증)
FROM   학번   A,
       자격증 B
WHERE  A.학번 = B.학번(+)
GROUP  BY A.학번

감사합니다~