create table citytime
(
ct_code     number(5)  primary key,
fd_code     number(5)  not null references flightdetails(fd_code) on delete cascade,
from_date   date null  ,
to_date     date null  ,
dep_time1   varchar2(5) not null,
dep_time2   varchar2(5),
dep_time3   varchar2(5),
dep_time4   varchar2(5),
arr_time2   varchar2(5) not null,
arr_time3   varchar2(5),
arr_time4   varchar2(5),
arr_time5   varchar2(5),
change_of_flight varchar2(1),
unique(fd_code,from_date,to_date)
)
/