Simple SQL query from table - sql

Question

For my CIS class, I have SQL project, and this is the first time I'm working with SQL, doing okay but I can't do one of the queries. Any help would be greatly appreciated.
This is what I tried:
Select cno, cname
from customer
where
)
)
)

Answer 1

Just use two IN clauses, one for 'Financial Accounting', one for 'Cost Accounting'.
Select cno, cname
from customer
where cno in
(
select cno
from salesorder
where ono in
(
select ono
from orderline
where bno in (select bno from book where bname = 'Financial Accounting')
)
)
and cno in
(
select cno
from salesorder
where ono in
(
select ono
from orderline
where bno in (select bno from book where bname = 'Cost Accounting')
)
);
Rob M's solution is more elegant, whereas above query should be more along the lines what you've learned so far.

Answer 2

You aren't exactly clear on whether the customer needs to have ordered both books in one order or across multiple orders. I'll assume the latter, based on the data provided.
Your answer returns customers who ordered either (or both) of those books. You say you want customers who order both books. Also, it's hard to keep your code straight when nesting several subqueries. Most people prefer joins.
This query should work for you.
select cno,cname from customer where cno in (
select o.cno
from salesorder o
inner join orderline ol on o.ono=ol.ono
inner join book b on b.bno=ol.bno
where b.bname in ('Financial Accounting', 'Cost Accounting')
group by o.cno
having count(distinct b.bno) = 2 -- Require both separate books, not 2 of one book or the other
)
Here is a complete example in SQL Server:
declare #book table (bno int, bname varchar(50))
insert #book (bno,bname) values
(10501,'Forensic Accounting')
,(10704,'Financial Accounting')
,(10933,'Cost Accounting')
declare #orderline table (ono int, bno int)
insert #orderline (ono,bno) VALUES
(1020,10501)
,(1020,10502)
,(1020,10503)
,(1020,10504)
,(1021,10605)
,(1022,10605)
,(1022,10704)
,(1023,10879)
,(1023,10988)
,(1024,10502)
,(1024,10988)
,(1026,10933)
,(1027,10933)
,(1028,10933)
,(1028,10965)
,(1029,10933)
,(1029,10965)
,(1029,10988)
,(1030,10965)
declare #salesorder table (ono int, cno int)
insert #salesorder (ono,cno) VALUES
(1020,23511)
,(1021,23513)
,(1022,23513)
,(1023,23512)
,(1024,23511)
,(1025,23511)
,(1026,23511)
,(1027,23512)
,(1028,23512)
,(1029,23513)
,(1030,23511)
declare #customer table (cno int, cname varchar(20))
insert #customer (cno,cname) values
(23511,'a')
,(23512,'b')
,(23513,'c')
,(23514,'d')
,(23515,'e')
,(23516,'f')
,(23517,'g')
,(23518,'h')
select cno,cname from #customer where cno in (
select o.cno
from #salesorder o
inner join #orderline ol on o.ono=ol.ono
inner join #book b on b.bno=ol.bno
where b.bname in ('Financial Accounting', 'Cost Accounting')
group by o.cno
having count(distinct b.bno) = 2 -- Require both separate books, not 2 of one book or the other
)