WITH book_t AS
(
SELECT 7825 membr_seq, '950106-00183EF' book, '2020-02-13 13:23' dt FROM dual
UNION ALL SELECT 2206, '950106-01847EF', '2020-02-13 14:36' FROM dual
UNION ALL SELECT 7826, 'K1049549EF'    , '2020-02-13 16:15' FROM dual
UNION ALL SELECT 2206, '950106-01231EF', '2020-02-13 16:15' FROM dual
UNION ALL SELECT 7826, 'K1049154EF'    , '2020-02-13 16:20' FROM dual
)
, log_t AS
(
SELECT 2206 membr_seq, '2020-02-13 17:43' dt FROM dual
UNION ALL SELECT 2206, '2020-02-13 17:43' FROM dual
UNION ALL SELECT 6784, '2020-02-13 17:43' FROM dual
UNION ALL SELECT 7825, '2020-02-13 17:44' FROM dual
UNION ALL SELECT 7825, '2020-02-13 17:44' FROM dual
UNION ALL SELECT 5002, '2020-02-13 17:49' FROM dual
UNION ALL SELECT 7826, '2020-02-13 17:50' FROM dual
UNION ALL SELECT 7826, '2020-02-13 17:50' FROM dual
UNION ALL SELECT 7826, '2020-02-13 17:50' FROM dual
UNION ALL SELECT 7826, '2020-02-13 17:50' FROM dual
)
SELECT b.book
     , COUNT(*) cnt
  FROM log_t a
     , (SELECT membr_seq, book
          FROM (SELECT membr_seq, book
                     , ROW_NUMBER() OVER(PARTITION BY membr_seq ORDER BY dt DESC) rn
                  FROM book_t
                )
         WHERE rn = 1
        ) b
 WHERE a.membr_seq = b.membr_seq(+)
 GROUP BY b.book
;

알려주신 쿼리로 해결할 수 있게 되었습니다.

도움 감사합니다.