title: Help with SQL query (Calculate a ratio between two entitiess)
body: <p>I’m going to calculate a ratio between two entities but are having some trouble with the query.</p>
  
  <p>The principal is the same to, say a forum, where you say:
  A user gets points for every new thread. Then, calculate the ratio of points for the number of threads.</p>
  
  <p>Example:
  User A has 300 points. User A has started 6 thread. The point ratio is: 50:6</p>
  
  <p>My schemas look as following:</p>
  
  <p>student(<strong>studentid</strong>, name, class, major)</p>
  
  <p>course(<strong>courseid</strong>, coursename, department)</p>
  
  <p>courseoffering(courseid, semester, year, <strong>instructor</strong>)</p>
  
  <p>faculty(<strong>name</strong>, office, salary)</p>
  
  <p>gradereport(<strong>studentid</strong>, <strong>courseid</strong>, semester, year, grade)</p>
  
  <p><em>The relations is a following:</em></p>
  
  <p>Faculity(name) = courseoffering(instructor)</p>
  
  <p>Student(studentid) = gradereport (studentid)</p>
  
  <p>Courseoffering(courseid) = course(courseid)</p>
  
  <p>Gradereport(courseid) = courseoffering(courseid)</p>
  
  <p>I have this query to select the faculty names there is teaching one or more students:</p>
  
  <pre><code>SELECT COUNT(faculty.name) FROM faculty, courseoffering, gradereport, student WHERE faculty.name = courseoffering.instructor AND courseoffering.courseid = gradereport.courseid AND gradereport.studentid = student.studentid
  </code></pre>
  
  <p>My problem is to find the ratio between the faculty members salary in regarding to the number of students they are teaching.</p>
  
  <p>Say, a teacher get 10.000 in salary and teaches 5 students, then his ratio should be 1:5.</p>
  
  <p>I hope that someone has an answer to my problem and understand what I'm having trouble with.</p>
  
  <p>Thanks</p>
  
  <p>Mestika</p>
  
  <p><strong>Some further explanation and examples on my problem and request:</strong></p>
  
  <p><strong>Employee 1:</strong> Salary = 10.000 | # of courses he teaches: 3 | # of students (totaly) following thoes 3 courses: 15.</p>
  
  <p>Then, Employee 1 earns 666,7 pr. each student. (i believe this is the ratio)</p>
  
  <p><strong>Employee 2:</strong> Salary = 30.000 | # of courses he teaches: 1 | # of students (totaly) following thoes 3 courses: 6.</p>
  
  <p>Then, Employee 2 earns 5000 pr. each student.</p>