I am trying to use
count() to count the number of the module where the particular student got the average mark below 40. It also needs to show the number 0 if the student does not have any assessment mark lower than 40. However, my query does not show any 0 number at all.
CREATE TABLE assessment ( assessmentId text, mark integer, studentId text, moduleId text, PRIMARY KEY (assessmentId, studentId, moduleId), FOREIGN KEY(studentId) REFERENCES student(studentId), FOREIGN KEY(moduleId) REFERENCES module(moduleId)) ";
in each record, it shows the module that the assessment is from, and show which student took the assessment.
this is my query
"select count(m.moduleId), avg(e.mark), m.studentId from assessment e left join assessment m on m.assessmentId = e.assessmentId and m.studentId = e.studentId and m.moduleId = e.moduleId group by m.studentId having avg(e.mark)<40";
the module could have more than one assessment, therefore the
avg(e.mark) is to find out the average mark for each module for each student. Therefore it is group by
so what i want the query to show is:
studentId|avg(e.mark)|count(m.moduleId) 1 | 50 | 0 2 | 20 | 2
However I am getting the result below
studentId|avg(e.mark)|count(m.moduleId) 1 | 20 | 2
I really don’t know where the problem is