WITH emp(empno, ename, reg_status) AS ( 
SELECT 1, '철수','임용' FROM dual UNION ALL
SELECT 2,'영희','임용'  FROM dual UNION ALL
SELECT 3,'민지','임용' FROM dual UNION ALL
SELECT 4,'AAA','' FROM dual)
, reg_status(empno, reg_yyyy, score) AS
( select 1, '2017', 3 from dual union all
select 2, '2018',8 from dual union all
select 3, '2017',4 from dual )
    
SELECT A.empno,A.ename
,MAX(B.score) KEEP (DENSE_rank FIRST order by reg_yyyy desc) as score
,MAX(B.reg_yyyy) KEEP (DENSE_rank FIRST order by reg_yyyy desc) as reg_yyyy
FROM emp      A
, reg_status  B
where A.empno= B.empno
and   A.reg_status = '임용'
group by A.empno,A.ename

또는

SELECT empno,ename, score, reg_yyyy
FROM (
        SELECT A.empno,A.ename, B.score, B.reg_yyyy
        ,row_number() OVER (PARTITION BY A.empno order by reg_yyyy desc) as rn
        FROM emp      A
        , reg_status  B
        where A.empno= B.empno
        and   A.reg_status = '임용'
      )
WHERE rn = 1;