select max value for each carID - sql

Question

I got three columns (carID, clientID, numClients). First one identifies a client, second one identifies a car and the third one shows how many times each client rented a car.
I need to get the maximum value of numClients for each carID.
I did this:
SELECT carID, clientID,
COUNT(*) AS numClients
FROM RENT R
JOIN DETAILS_OF_RENT D ON d.rentID = r.ID
GROUP BY carID, clientID
ORDER BY carID, clientID;
So the table I get is something like this:
+---------+----------+------------+
| carID | clientID | numClients |
+---------+----------+------------+
| 0765BBC | C02 | 1 |
| 0765BBC | C05 | 1 |
| 0765BBC | C07 | 1 |
| 0765BBC | C13 | 1 |
| 0765BBC | C14 | 1 |
| 1234XQP | C01 | 1 |
| 1234XPQ | C02 | 1 |
| 1234XPQ | C07 | 1 |
| 1234XPQ | C09 | 2 |
| 1234XPQ | C11 | 1 |
| 1523BBD | c07 | 1 |
| 1523BBD | c09 | 2 |
+---------+----------+------------+
My output should be 0765BBC and 1523BBD since they we're rented by the same client 2 times.
So, I have to get the carID's of the cars which were rented by the same client more times but I don't know how to select these rows from the above table

Answer 1

You appear to want something like this:
SELECT rd.*
FROM (SELECT rd.*, DENSE_RANK() OVER (ORDER BY client_cnt DESC) as seqnum
FROM (SELECT carID, clientID, COUNT(*) OVER (PARTITION BY clientId) as client_cnt
FROM RENT R JOIN
DETAILS_OF_RENT D
ON d.rentID = r.ID
) rd
) rd
WHERE seqnum = 1;
I don't think aggregation is needed. The innermost subquery adds a column which is the total number of cars for each client. The middle subquery adds a column which identifies the biggest values. The outer query then chooses the largest values.