Table Joining Issues - sql

Question

I have difficulties joining the tables below for the desired query as stated.
Theatre (Theatre#, Name, Address, MainTel);
Production (P#, Title, ProductionDirector, PlayAuthor);
Performance (Per#, P#, Theatre#, pDate, pHour, pMinute, Comments);
Client (Client#, Title, Name, Street, Town, County, telNo, e-mail);
Ticket Purchase (Purchase#, Client#, Per#, PaymentMethod, DeliveryMethod, TotalAmount)
Required Query
The theater name (for each theater) and the names of clients who have the highest spending in that theater
SELECT T.NAME, C.NAME, SUM(TOTALAMOUNT)
FROM TICKETPURCHASE TP,
THEATRE T,
CLIENT C,
PERFORMANCE PER
WHERE TOTALAMOUNT = (SELECT MAX (TOTALAMOUNT)
FROM TICKETPURCHASE TP2,
THEATRE T2,
PERFORMANCE PER2,
CLIENT C2,
PRODUCTION P2
WHERE T2.NAME = T.NAME
AND T2.THEATRE# = PER2.THEATRE#
AND TP2.CLIENT# = C2.CLIENT#
AND TP2.PER# =PER2.PER#
AND PER2.P# = P2.P# )
AND C.CLIENT# = TP.CLIENT#
AND T.THEATRE# = PER.THEATRE#
AND TP.PER# = PER.PER#
AND PER.P# = P.P#
GROUP BY T.NAME, C.NAME, TOTALAMOUNT

Answer 1

From Oracle 12, you can do it all in a single query if you aggregate by the primary keys for the theatre and the client to get the total spent and then rank the spending in the ORDER BY clause and use the row limiting clause to get the first ranked values:
SELECT MAX(T.NAME) AS theatre_name,
MAX(C.NAME) AS client_name,
SUM(TP.TOTALAMOUNT) AS amount_spent
FROM TICKETPURCHASE TP
INNER JOIN PERFORMANCE PER
ON (TP.PER# = PER.PER#)
INNER JOIN THEATRE T
ON (T.THEATRE# = PER.THEATRE#)
INNER JOIN CLIENT C
ON (C.CLIENT# = TP.CLIENT#)
GROUP BY
T.THEATRE#,
C.CLIENT#
ORDER BY
DENSE_RANK() OVER (
PARTITION BY T.THEATRE#
ORDER BY SUM(TP.TOTALAMOUNT) DESC
)
FETCH FIRST ROW WITH TIES;
In earlier versions, you can use the same technique and filter in an outer query:
SELECT theatre_name,
client_name,
amount_spent
FROM (
SELECT MAX(T.NAME) AS theatre_name,
MAX(C.NAME) AS client_name,
SUM(TP.TOTALAMOUNT) AS amount_spent,
DENSE_RANK() OVER (
PARTITION BY T.THEATRE#
ORDER BY SUM(TP.TOTALAMOUNT) DESC
) As rnk
FROM TICKETPURCHASE TP
INNER JOIN PERFORMANCE PER
ON (TP.PER# = PER.PER#)
INNER JOIN THEATRE T
ON (T.THEATRE# = PER.THEATRE#)
INNER JOIN CLIENT C
ON (C.CLIENT# = TP.CLIENT#)
GROUP BY
T.THEATRE#,
C.CLIENT#
)
WHERE rnk = 1;