Hi,
I've got a table which models the relationship between flights and
legs, which is defined like this:-
create table flight_leg ( flight_id integer references flight(id), leg_id integer references leg(id)
);
One leg may be part of many flights and one flight may be made up of 1
or more legs.
I also have a table which maps flights to comparable flights. The
mapping is created manually. It is defined like this:-
create table cmp_flight ( flight_id integer references flight(id), cmp_flight_id integer references flight(id)
);
The flight and leg tables referenced are omitted for brevity.
I want to be able to show all the flight_ids and their leg counts as
well as the cmp_flight_ids and leg counts.
e.g.
insert into flight_legs values (1, 1);
insert into flight_legs values (1, 2);
insert into flight_legs values (2, 3);
insert into flight_legs values (2, 4);
insert into flight_legs values (2, 5);
insert into flight_legs values (3, 3);
insert into flight_legs values (4, 1);
insert into flight_legs values (5, 3);
insert into flight_legs values (5, 4);
insert into flight_legs values (6, 4);
insert into flight_legs values (7, 5);
insert into cmp_flight values (1, 2);
insert into cmp_flight values (1, 3);
insert into cmp_flight values (4, 5);
insert into cmp_flight values (4, 6);
insert into cmp_flight values (4, 7);
The result I'm looking for is
flight_id num_legs cmp_flight_id cmp_num_legs
1 2 2 3
1 2 3 1
4 1 5 2
4 1 6 1
4 1 7 1
This does the trick:-
select cf.flight_id, tl1.num_legs, cf.cmp_flight_id, tl2.num_legs cmp_num_legs
from cmp_flight cf join (select fl1.flight_id fid1, count(*) num_legs from flight_leg fl1 group by
fl1.flight_id)tl1 on fid1 = cf.flight_id join (select fl2.flight_id fid2, count(*) num_legs from flight_leg fl2
groupby fl2.flight_id) tl2 on fid2 =
cf.cmp_flight_id;
Is this a better way to go about it?
I've considered keeping a track of the number of legs in the flight
table, using a trigger, but it doesn't seem relationally 'clean'.
Kind Regards,
Steve Sabljak
