如何在我的 SQL function 中使用 MAX ( COUNT (*))？

Question

SELECT F.origin, F.destination, COUNT(DISTINCT E.ename), COUNT(F.flno)
FROM Flights F, Employees E, Certified C, Aircraft A
WHERE E.eid = C.eid AND E.salary > 100000 AND A.aid = C.aid AND F.distance >= A.cruisingrange
GROUP BY E.ename, F.origin, F.destination
HAVING (COUNT(F.flno)) = 14

The thing is that 14 is the max(count(F.flno)) of the table but I don't know how to transform all of this to replace that 14 for the maximum number of a column based on COUNT(F.flno)

Answer 1

Here is a way to do this, in sql server, in other databases there would be the top equivalent which you can check.

 with source_qry
   as(
    SELECT F.origin, F.destination, COUNT(DISTINCT E.ename), COUNT(F.flno) as cnt_flno
      FROM Flights F, 
           Employees E, 
           Certified C, 
           Aircraft A
     WHERE E.eid = C.eid 
       AND E.salary > 100000 
       AND A.aid = C.aid 
       AND F.distance >= A.cruisingrange
    GROUP BY E.ename, F.origin, F.destination
         )
select top 1* 
  from source_qry
order by cnt_flno desc

Answer 2

SELECT F.origin, F.destination, COUNT(DISTINCT E.ename), COUNT(F.flno)
FROM Flights F, Employees E, Certified C, Aircraft A
WHERE E.eid = C.eid AND E.salary > 100000 AND A.aid = C.aid AND F.distance >= A.cruisingrange
GROUP BY E.ename, F.origin, F.destination
ORDER BY 4 DESC
LIMIT 1;

Answer 3

WITH data AS (
    SELECT F.origin, F.destination, COUNT(DISTINCT E.ename) AS cnt_ename, COUNT(F.flno) AS cnt,
        MAX(COUNT(F. flno)) OVER () AS maxcnt
    FROM Flights F, Employees E, Certified C, Aircraft A
    WHERE E.eid = C.eid AND E.salary > 100000 AND A.aid = C.aid AND F.distance >= A.cruisingrange
    GROUP BY E.ename, F.origin, F.destination
)
SELECT * FROM data WHERE cnt = maxcnt;

This will handle ties in the maximum count. Get away from the habit of using top and limit indiscriminately.