로직은
일수 - 1주당2일 - 시작요일별 나머지일수별 토/일수

SELECT DY_CNT - TRUNC(DY_CNT/7)*2 -
       CASE STR_D||MOD(DY_CNT,7)  WHEN '11' THEN 1
                                  WHEN '12' THEN 1
                                  WHEN '13' THEN 1
                                  WHEN '14' THEN 1
                                  WHEN '15' THEN 1
                                  WHEN '16' THEN 1
                                  WHEN '26' THEN 1
                                  WHEN '35' THEN 1
                                  WHEN '36' THEN 2
                                  WHEN '44' THEN 1
                                  WHEN '45' THEN 2
                                  WHEN '46' THEN 2
                                  WHEN '53' THEN 1
                                  WHEN '54' THEN 2
                                  WHEN '55' THEN 2
                                  WHEN '56' THEN 2
                                  WHEN '62' THEN 1
                                  WHEN '63' THEN 2
                                  WHEN '64' THEN 2
                                  WHEN '65' THEN 2
                                  WHEN '66' THEN 2
                                  WHEN '71' THEN 1
                                  WHEN '72' THEN 2
                                  WHEN '73' THEN 2
                                  WHEN '74' THEN 2
                                  WHEN '75' THEN 2
                                  WHEN '76' THEN 2
                                  ELSE 0
       END workday
FROM  (
      SELECT  TO_CHAR(TO_DATE(:STR_DT, 'YYYYMMDD'), 'D') STR_D
             ,TO_DATE(:END_DT, 'YYYYMMDD') -  TO_DATE(:STR_DT, 'YYYYMMDD')+1 DY_CNT
      FROM   DUAL
      )

Connect By Level < n 를 이용한 행 복제 방법은
Dual 과 같이 1 Row 데이터에만 적용하는 방법입니다.
여러행의 자료에 적용하면 예상건수보다 훨씬 더 많이 나오게 되며
건수가 많을 수록 응답이 안나올 수 있습니다.
아래 사이트 참고하시면 될듯 합니다.
http://www.oracleclub.com/article/51663