WITH holiday AS
(
SELECT 1 id, '2018-07-03' dt FROM dual
UNION ALL SELECT 2, '2018-07-17' FROM dual
)
, request AS
(
SELECT 1 id, '2018-07-02' reg_dt,  7 work_day FROM dual
UNION ALL SELECT 2, '2018-07-05',  7 FROM dual
UNION ALL SELECT 3, '2018-07-11', 14 FROM dual
)
-- 1. 행복제 방법 --
SELECT id, reg_dt, work_day
     , TO_CHAR(TO_DATE(reg_dt, 'yyyy-mm-dd') + lv, 'yyyy-mm-dd') limit_dt
  FROM (SELECT a.id, a.reg_dt, a.work_day
             , b.lv
             , c.dt
             , ROW_NUMBER() OVER(PARTITION BY a.id ORDER BY b.lv) rn
          FROM request a
         CROSS JOIN (SELECT LEVEL lv FROM dual CONNECT BY LEVEL <= 99) b
          LEFT OUTER JOIN holiday c
            ON TO_CHAR(TO_DATE(a.reg_dt, 'yyyy-mm-dd') + b.lv, 'yyyy-mm-dd') = c.dt
         WHERE c.dt IS NULL
           AND TO_CHAR(TO_DATE(a.reg_dt, 'yyyy-mm-dd') + b.lv, 'd') NOT IN ('1', '7')
        )
 WHERE work_day = rn
;

WITH holiday AS
(
SELECT 1 id, '2018-07-03' dt FROM dual
UNION ALL SELECT 2, '2018-07-17' FROM dual
)
, request AS
(
SELECT 1 id, '2018-07-02' reg_dt,  7 work_day FROM dual
UNION ALL SELECT 2, '2018-07-05',  7 FROM dual
UNION ALL SELECT 3, '2018-07-11', 14 FROM dual
)
-- 2. Recursive WITH
, tmp(id, reg_dt, work_day, lv, cnt) AS
(
SELECT a.id, a.reg_dt, a.work_day
     , 0 lv
     , 0 cnt
  FROM request a
 UNION ALL
SELECT a.id, a.reg_dt, a.work_day
     , a.lv + 1 lv
     , a.cnt
     + CASE WHEN b.dt IS NOT NULL
              OR TO_CHAR(TO_DATE(a.reg_dt, 'yyyy-mm-dd') + a.lv + 1, 'd') IN ('1','7')
            THEN 0 ELSE 1 END cnt
  FROM tmp a
  LEFT OUTER JOIN holiday b
    ON TO_CHAR(TO_DATE(a.reg_dt, 'yyyy-mm-dd') + a.lv + 1, 'yyyy-mm-dd') = b.dt
 WHERE a.cnt < a.work_day
)
SELECT id, reg_dt, work_day
     , TO_CHAR(TO_DATE(reg_dt, 'yyyy-mm-dd') + lv, 'yyyy-mm-dd') limit_dt
  FROM tmp
 WHERE cnt = work_day
;

-- 일자로 계산했어요 박으로 계산하려면 -1 하셔야할듯합니다.
WITH HOLIDAY AS (
SELECT 1 SEQ , TO_DATE('2018-07-03','YYYY-MM-DD') DT FROM DUAL UNION ALL
SELECT 2 , TO_DATE('2018-07-17','YYYY-MM-DD') FROM DUAL 
) , T AS (
SELECT 1 SEQ , TO_DATE('2018-07-02','YYYY-MM-DD') ST_DT , TO_DATE('2018-07-12','YYYY-MM-DD') ED_DT FROM DUAL UNION ALL
SELECT 2 , TO_DATE('2018-07-05','YYYY-MM-DD') ST_DT , TO_DATE('2018-07-16','YYYY-MM-DD') ED_DT FROM DUAL UNION ALL
SELECT 3 , TO_DATE('2018-07-11','YYYY-MM-DD') ST_DT , TO_DATE('2018-08-01','YYYY-MM-DD') ED_DT FROM DUAL 
)
SELECT  Z.SEQ , Z.ST_DT , Z.ED_DT , COUNT(*) "처리일자"
  FROM (SELECT A.SEQ , ST_DT  , ED_DT , ST_DT + LV - 1 AS DD
          FROM T A
             , (SELECT LEVEL LV  FROM DUAL CONNECT BY LEVEL <= 30 ) B
         WHERE B.LV < ( A.ED_DT - A.ST_DT + 1 ) + 1 
         ORDER BY A.SEQ  , 4
       ) Z
 WHERE NOT EXISTS ( SELECT 'X' FROM HOLIDAY H WHERE H.DT = Z.DD ) 
   AND TO_CHAR(Z.DD,'D') NOT IN ( 7 , 1 ) 
 GROUP BY Z.SEQ , Z.ST_DT , Z.ED_DT  

먼저 함수를 만들고

CREATE OR REPLACE function f_get_subdays (
         pSTR     IN VARCHAR2
       , pDAYS     IN VARCHAR2
)
return varchar2
is
ret_val     varchar2(10) := '';
vDATE          varchar2(10) := '';
vDAYS         number       := 0 ;
begin

    FOR I IN 0..999999 LOOP
       if to_char(to_date(pSTR,'YYYYMMDD') + I,'d') not in ('1','7') then
          vDAYS := vDAYS + 1;
          vDATE := to_char(to_date(pSTR,'YYYYMMDD') + I,'YYYYMMDD');
       end if;
       
       if vDAYS >= to_number(pDAYS) then 
         ret_val := vDATE;
         goto RTN;
       end if;
    END LOOP;
     
<<RTN>>     
    return ret_val;

    exception
    when no_data_found then
        return 0 ;

end ;
/

이런형식으로 call 하면 될거 같습니다.

select f_get_subday('20180701','11') from dual;

다들 감사합니다!