在2个级别上对SQL排名

Question

Okay, another SQL question. What I am trying to achieve is to show by company, which courses their employees have been to, and from there, which is the most popular for each company.
Currently, this is what I have:

SELECT a.corporatename, e.course_title, b.studentID FROM corporate a
JOIN students b ON a.corporateID = b.corporateID
JOIN studentcoursedetails c ON b.studentID = c.studentID
JOIN classdetails d ON c.classdetailID = d.classdetailID
JOIN course e ON d.courseID = e.courseID
WHERE b.corporateID != '0'
ORDER BY a.corporatename, e.course_title

This gives me something along these lines:

corporatename ----------------------------- course_title --------------------------------- studentID
Deutsche Lufthansa AG Berlin ----- Airline Security Operations --------- 5
Deutsche Lufthansa AG Berlin ----- Airline Security Operations --------- 6
Deutsche Lufthansa AG Berlin ----- Airline Security Operations --------- 5
Deutsche Lufthansa AG Berlin ----- Workshop on Crisis Management ------ 6
Deutsche Lufthansa AG Berlin ----- Workshop on Crisis Management ------ 7
Korean Air Lines Co., Ltd ---------- Airline Security Operations --------- 8

From the above, we can see that Lufthansa has sent it's employees to 2 courses so far. Even though studentID 5 has been to a particular course twice, because he flunked the first try, it is recorded as 2 entries.

What I hope to attain is this:

Deutsche Lufthansa AG Berlin ----- Airline Security Operations --------- 3
Deutsche Lufthansa AG Berlin ----- Workshop on Crisis Management ------ 2
Korean Air Lines Co., Ltd ---------- Airline Security Operations --------- 1

I tried to use this code:

SELECT a.corporatename, e.course_title, count( DISTINCT b.studentID ) AS total
FROM corporate a
JOIN students b ON a.corporateID = b.corporateID
JOIN studentcoursedetails c ON b.studentID = c.studentID
JOIN classdetails d ON c.classdetailID = d.classdetailID
JOIN course e ON d.courseID = e.courseID
WHERE b.corporateID != '0'
GROUP BY a.corporatename
ORDER BY a.corporatename, e.course_title

But what I got:

corporatename ----------------------------- course_title --------------------------------- total
Deutsche Lufthansa AG Berlin ----- Workshop on Crisis Management ------ 3
Korean Air Lines Co., Ltd ---------- Airline Security Operations --------- 1

it shows me the most popular, yes, but I'd like to be able to compare all ranks.
I'd appreciate any help on this.

Thanks to bluish , a simple solution.

SELECT a.corporatename, e.course_title, count( b.studentID ) AS total
FROM corporate a
JOIN students b ON a.corporateID = b.corporateID
JOIN studentcoursedetails c ON b.studentID = c.studentID
JOIN classdetails d ON c.classdetailID = d.classdetailID
JOIN course e ON d.courseID = e.courseID
WHERE b.corporateID != '0'
GROUP BY a.corporatename , e.course_title
ORDER BY a.corporatename, e.course_title

I removed the DISTINCT because I need to collect data of all enrollments, not each unique user. Thanks.

Answer 1

Try to add also e.course_title in the GROUP BY:

SELECT a.corporatename, e.course_title, count( DISTINCT b.studentID ) AS total
FROM corporate a
JOIN students b ON a.corporateID = b.corporateID
JOIN studentcoursedetails c ON b.studentID = c.studentID
JOIN classdetails d ON c.classdetailID = d.classdetailID
JOIN course e ON d.courseID = e.courseID
WHERE b.corporateID != '0'
GROUP BY a.corporatename, e.course_title
ORDER BY a.corporatename, e.course_title