Database query- find most expensive part - sql

Question

Here is my schema
Suppliers(​sid ,​sname,address)
Cata(sid,pid,cost)
Parts(pid,pname,color)
bolded are primary keys
I am trying to write a query
"Find the pids of the most expensive parts"
I am using set difference here is my query however its returning all the pids in the catalogue not the one with the highest cost
select Cata.pid
from Cata
where pid not in(
select c.pid
from Cata c, Cata f
where c.sid=f.sid AND c.pid=f.pid AND c.cost<f.cost
);

Answer 1

Try this one:
select c1.pid
from Cata c1
where not exists (
select c2.pid
from Cata c2
where c2.cost > c1.f.cost
);
If you are wondering what is wrong with your query, notice that the inner SELECT is returning 0 rows, because you are comparing the cost of the items with themselves, so c.cost is always equal to f.cost, so the < comparation fails, so the inner select returns 0 rows, so the "not in" condition is true for all the rows

Answer 2

If you want the pid with the single highest cost:
SELECT TOP 1 WITH TIES
c.pid,
c.cost
FROM
Cata AS c
ORDER BY
c.cost DESC
If you want the five highest cost pids, change the first line of that to:
SELECT TOP 5 WITH TIES

Answer 3

I think this is what you are looking for
SELECT
p.PID
, MAX(c.COST)
FROM
Parts p
LEFT JOIN
Cata c
ON p.PID = c.PID
GROUP BY
p.PID
ORDER BY
MAX(c.COST)
This will return you the most expensive part per PID
Good luck!

Answer 4

You want to
Find the pids of the most expensive parts
As you have not mentioned your requirement clearly,
I have given 2 solutions
Solution 1 : to find most expansive parts for each supplier
Solution 2 : to find most expensive part amongst all the parts
Use which ever suits you.
Solution 1:
SELECT Cata.pid FROM Cata
LEFT OUTER JOIN (SELECT Cata.sid, MAX(Cata.cost) cost FROM Cata GROUP BY Cata.sid) MostExpensive
ON Cata.sid = MostExpensive.sid AND Cata.cost = MostExpensive.cost
Query explanation:
First you should try to find what is most expensive as per cost for each sid
then once you have that got that most expensive table derived, find pids which matches the cost in the same sid.
If there is a tie between 2 parts for being most expensive, this query will return pids for both the parts.
Solution 2:
If you looking for most expansive parts across all the suppliers then query could be simplified as below.
SELECT Cata.pid FROM Cata
WHERE Cata.cost = (SELECT MAX(cost) cost FROM Cata)

Answer 5

Find the pids of the most expensive parts
The most expensive parts are the ones where the minimum cost is highest, i.e. you can get all other parts cheaper than these ones where you must at least pay xxx $. You get these with a top query.
select top(1) with ties
pid
from cata
group by pid
order by min(cost) desc;
Illustration:
pid | supplier A | supplier B | supplier C
----+------------+------------+-----------
p1 | 10$ | 10$ | 100$
p2 | 40$ | 50$ | 60$
Which part is the more expensive one? I can buy p1 for 10$. For p2 I must pay at least 40$. So p2 is more expensive. That supplier C wants an outrageous 100$ for p1 doesn't matter, because who would pay 100$ for something you can get for 10$? So it's the minimum prices we must compare.