Я думаю, вы могли бы сделать это с дополнительным шагом, подобным этому:
SQL> ALTER SESSION SET nls_date_format='dd/mm/yyyy hh24:mi';
Session altered
SQL> with my_data as (
2 SELECT to_date('02/01/2011') my_date, to_date('02/01/2011 05:45') DEP_DT, 177 LOG_NO, 157511995 LEG_NO, 'ANTONI,BARFAR,GARGNI' CREW FROM DUAL
3 UNION ALL SELECT to_date('02/01/2011'), to_date('02/01/2011 08:40'), 177, 157512040, 'ANTONI,BARFAR,GARGNI' FROM DUAL
4 UNION ALL SELECT to_date('02/01/2011'), to_date('02/01/2011 06:35'), 179, 157556684, 'GGNCNI,HULBRA,LIFEDA' FROM DUAL
5 UNION ALL SELECT to_date('02/01/2011'), to_date('02/01/2011 09:10'), 179, 157556773, 'GGNCNI,HULBRA,LIFEDA' FROM DUAL
6 UNION ALL SELECT to_date('02/01/2011'), to_date('02/01/2011 11:40'), 179, 157534059, 'GGNCNI,HULBRA,LIFEDA' FROM DUAL
7 UNION ALL SELECT to_date('02/01/2011'), to_date('02/01/2011 14:10'), 179, 157533956, 'GGNCNI,HULBRA,LIFEDA' FROM DUAL
8 UNION ALL SELECT to_date('02/01/2011'), to_date('02/01/2011 17:00'), 179, 157542667, 'AINGHI,BOIGDE,MORWRE' FROM DUAL
9 UNION ALL SELECT to_date('02/01/2011'), to_date('02/01/2011 19:55'), 179, 157542712, 'AINGHI,BOIGDE,MORWRE' FROM DUAL
10 )
11 SELECT my_date, dep_dt, log_no, leg_no, crew,
12 dense_rank() over(PARTITION BY my_date, log_no ORDER BY min_dt, crew) dr
13 FROM (SELECT d.*,
14 MIN(dep_dt) over(PARTITION BY my_date, log_no, crew) min_dt
15 FROM my_data d);
MY_DATE DEP_DT LOG_NO LEG_NO CREW DR
----------- ----------- ---------- ---------- -------------------- ----------
02/01/2011 02/01/2011 177 157512040 ANTONI,BARFAR,GARGNI 1
02/01/2011 02/01/2011 177 157511995 ANTONI,BARFAR,GARGNI 1
02/01/2011 02/01/2011 179 157556684 GGNCNI,HULBRA,LIFEDA 1
02/01/2011 02/01/2011 179 157556773 GGNCNI,HULBRA,LIFEDA 1
02/01/2011 02/01/2011 179 157533956 GGNCNI,HULBRA,LIFEDA 1
02/01/2011 02/01/2011 179 157534059 GGNCNI,HULBRA,LIFEDA 1
02/01/2011 02/01/2011 179 157542667 AINGHI,BOIGDE,MORWRE 2
02/01/2011 02/01/2011 179 157542712 AINGHI,BOIGDE,MORWRE 2
8 rows selected