CISC 7510X Midterm Exam
1 c
2 b
3 d
4 b
5 a
6 d
7 d
8 a
9 c
10 c
11 d
12 c
13 a
14 d
15 e
16 e
17 e
18 a
19 b
20 c

15: Note, your code may (and likely will) be different:
with icost as (
    select iid, sum(price) cost, avg( sum(price) ) over () avgcost
    from itinerary natural inner join itineraryitem
    group by iid
)
select sum(case when cost > avgcost then 1.0 else 0.0 end)/sum(1.0)*100
from icost

16: Note, your code may (and likely will) be different: 
select distinct tid
from itinerary
    natural inner join itineraryitem
    natural inner join flight
where 
    flightno='ABC123' and 
    departtim >= cast('2015-01-01' as date) and
    departtim <  cast('2015-02-01' as date)

17: Note, your code may (and likely will) be different:
with tidflight as (
    select distinct tid,flightno
    from itinerary
        natural inner join itineraryitem
        natural inner join flight
    where flightno in ('ABC123','XYZ789')
)
select tid
from tidflight 
group by tid
having count(*) > 1