Question

Right now, I have a query that gets me 3 columns.

SELECT a.studentID, a.classdetailID, c.course_title
FROM studentcoursedetails a, classdetails b, course c
WHERE b.classdetailID = a.classdetailID
AND b.courseID = c.courseID
ORDER BY c.course_title, b.classdetailID

What I get is a column that shows the ID of the student that did the course, the ID of the class they were in and the title of the course itself. Something along these lines:

5---8----Airline Security Operations  
4---8----Airline Security Operations  
6---8----Airline Security Operations  
4---9----Airline Security Operations  
8---10---Airline Security Operations  
5---10---Airline Security Operations  
1---1----Airport Design and Construction  
4---1----Airport Design and Construction  
2---1----Airport Design and Construction  
1---2----Airport Design and Construction

What I need is a table that shows me something like this:

course_title                Number of Classes  Number of students
Airline Security Operations   3                   4

I thought of using CASE, but when I think about it, I just get lost. I’d appreciate your help.

The answer, thanks to gbn:

SELECT c.course_title, COUNT( DISTINCT a.studentID ) AS “Students in Course” , COUNT( DISTINCT a.classdetailID ) AS “Total Classes”
FROM studentcoursedetails a
JOIN classdetails b ON b.classdetailID = a.classdetailID
JOIN course c ON b.courseID = c.courseID
GROUP BY c.course_title

Answer 1

You want to count each distinct occurence per course_title

Like this (with SQL Server column alias syntax) with proper JOIN syntax

SELECT
    c.course_title
    ,COUNT(DISTINCT a.studentID) AS [Number of students that have taken the course]
    ,COUNT(DISTINCT a.classdetailID) AS [Number of Classes]
FROM
    studentcoursedetails a
    JOIN
    classdetails b ON b.classdetailID = a.classdetailID
    JOIN
    course c ON b.courseID = c.courseID
GROUP BY
    c.course_title