SQL inquiry, tried absolutely everything I know, sql, four tables - sql

Question

I cant get this inquiry, tried like every thing
TABLE: ARTIST
JMBG NAME AGE ADRESA
--------------------------------------
J1 Ladygaga 35 HOLIVUDHILZ
J2 DUSKO 13 BB
J3 EMINEM 40 REVOLUCIJA 5
J4 BAGI 22 KURAC
J5 MARKO 33 ULICA
TABLE:HALL
DID CAPACITY CITY
---------------------------------
D1 500 PODGORICA
D2 300 NIS
D3 1000 BAR
D4 2000 NEWYORK
D5 750 BEOGRAD
TABLE: CITY
-----------------------------------------
BAR montenegro 5000
BEOGRAD Serbia 2000000
BUDVA montenegro 50000
NEWYORK AMERICA 7000000
NIS Serbia 1000000
PODGORICA montenegro 250000
TABLE: CONCERT
ID JMBG HALL
------------------------
K1 J3 D4
K2 J4 D1
K3 J1 D1
K4 J1 D5
K5 J1 D1
K6 J3 D1
K7 J5 D1
The inquiry is: Find the countries where the artist with the most held concerts
has performed in. I really did spend a lot of time on this and energy. I would greatly appreciate if someone could do this that has experience, and doesnt find it too difficult.
I tried this:
SELECT DISTINCT COUNTRY FROM CITY G, HALL D, CONCERT K
WHERE K.DID = D.DID AND D.NAZIV = G.NAZIV AND EXISTS(
SELECT JMBG FROM CONCERT K1,HALL D1, CITY G1
WHERE K.KID=K1.KID
GROUP BY JMBG
HAVING COUNT (*) >= ALL(SELECT COUNT(*) FROM CONCERT
GROUP BY JMBG))

Answer 1

Break it down. The artist with the most held concerts... Which artist had the most held concerts? (We're going to assume that we're interested in the total number of concerts held overall (in all countries), not the number of concerts held in a particular country.
How many concerts did each artist hold?
SELECT c.jmbg
, COUNT(1) AS cnt
FROM concert c
GROUP BY c.jmbg
Which artist held the most concerts? MySQL and MS SQL Server both have some convenient short cuts we can use here. A question we should ask here, what if there are two or more artists held the same number of concerts? Do we want to return both (or all) of those artists, or just return one of them? Which one? (We'd prefer the query to be deterministic... to return the same result given the same rows in the tables.)
Assuming that we want to return just one artist that held the most concerts...
For MySQL:
SELECT c.jmbg
FROM concert c
GROUP BY c.jmbg
ORDER BY COUNT(1) DESC, c.jmbg DESC
LIMIT 1
For SQL Server:
SELECT TOP 1 c.jmbg
FROM concert c
GROUP BY c.jmbg
ORDER BY COUNT(1) DESC, c.jmbg DESC
So that gets us the artist.
The other part of the "inquiry"... which countries did the artist hold concerts in.
Given a particular artist, we could write a query that performs join operations on the concert, hall and city tables. We'll just take a guess at the name of that first column in the city table (since it isn't provided in the question).
SELECT i.country
FROM city i
JOIN hall h
ON h.city = i.cid
JOIN concert o
ON o.hall = h.did
WHERE o.jmbg = 'Ladygaga'
GROUP BY i.country
To combine the two queries, we could use the first as a subquery. My preference is to use an inline view.
SELECT g.country
FROM city g
JOIN hall h
ON h.city = g.cid
JOIN concert o
ON o.hall = h.did
JOIN (
SELECT c.jmbg
FROM concert c
GROUP BY c.jmbg
ORDER BY COUNT(1) DESC, c.jmbg DESC
LIMIT 1
) m
ON m.jmbg = o.jmbg
GROUP BY g.country
Obviously, there are obviously other query patterns that will return an equivalent result.
As I noted in a comment on the question, the specification for this "inquiry" is a bit ambiguous, as to what is meant by "where the artist with the most held concerts has performed in".
There is another interpretation of that specification. If we're interested in getting and analyzing a count of "how many concerts were held in each country by each artist", that's a different query.
FOLLOWUP
"... not allowed to use TOP DESC"
Then just write the query differently. Here's a different way to get the "largest number of concerts held by any artist", and use that to get all the artists that all held that number of concerts.
SELECT n.jmbg
FROM ( -- largest number of concerts by artist
SELECT MAX(p.cnt) AS maxcnt
FROM (
SELECT COUNT(1) AS cnt
FROM concert d
GROUP BY d.jmbg
) p
) o
JOIN ( -- count of concerts by artist
SELECT c.jmbg
, COUNT(1) AS cnt
FROM concert c
GROUP BY c.jmbg
) n
ON n.cnt = o.maxcnt
Since that has the potential to return more than one row (more than one artist), your outer query may want to return a list of countries for each of the returned artists. That is to say, rather than just GROUP BY g.country, you'll likely want to return the artist in the SELECT list, and
GROUP BY m.jmbg, g.country
ORDER BY m.jmbg, g.country

Answer 2

This is a basic question that looks like coming out of school type of question. This answer will give you some hints but you need to work it out for yourself.
JOIN is your friend, find source below:
JOIN - MySQL
JOIN - SQL Server
What you need to do:
join CONCERT table with HALL table by HALL ID
join HALL table to CITY table by CITY name
sum the count of country appearance or hall capacity (either one you need) grouped by artist
order descending by the sum of count if you need it
Good luck