WITH code_t AS
(
SELECT 1 lv, 0 s, 20 e,'20세이하' gb FROM dual
UNION ALL SELECT 2, 21, 25, '21~25'    FROM dual
UNION ALL SELECT 3, 26, 30, '26~30'    FROM dual
UNION ALL SELECT 4, 31, 35, '31~35'    FROM dual
UNION ALL SELECT 5, 36, 40, '36~40'    FROM dual
UNION ALL SELECT 6, 46, 50, '46~50'    FROM dual
UNION ALL SELECT 7, 51, 55, '51~55'    FROM dual
UNION ALL SELECT 8, 56, 99, '56세이상' FROM dual
)
SELECT NVL(a.gb, '(총계)') gb
     , COUNT(x) tot
     , COUNT(DECODE(x, 0, 1)) "0"
     , COUNT(DECODE(x, 1, 1)) "1"
     , COUNT(DECODE(x, 2, 1)) "2"
     , COUNT(DECODE(x, 3, 1)) "3"
     , COUNT(DECODE(x, 4, 1)) "4"
     , COUNT(DECODE(x, 5, 1)) "5"
     , COUNT(DECODE(x, 6, 1)) "6"
     , COUNT(DECODE(x, 7, 1)) "7"
     , COUNT(DECODE(x, 8, 1)) "8"
     , COUNT(DECODE(x, 9, 1)) "9"
     , COUNT(CASE WHEN x BETWEEN 10 AND 14 THEN 1 END) "10~"
     , COUNT(CASE WHEN x BETWEEN 15 AND 19 THEN 1 END) "15~"
     , COUNT(CASE WHEN x >= 20             THEN 1 END) "20~"
  FROM code_t a
     , (SELECT FLOOR(MONTHS_BETWEEN(TRUNC(sysdate), TO_DATE(enter_dt, 'yyyymmdd')) / 12) x -- 근속년
             , FLOOR(MONTHS_BETWEEN(TRUNC(sysdate), TO_DATE(birth_dt, 'yyyymmdd')) / 12) y -- 만나이
          FROM emp
         WHERE retire_dt IS NULL  -- 퇴직자 제외
        ) b
 WHERE b.y(+) BETWEEN a.s AND a.e
 GROUP BY ROLLUP((a.lv, a.gb))
 ORDER BY lv
;