Is my solution to this SQL query correct? - mysql

Question

In my exam we were given the following relations:
COURSES(**Number**, School, CourseName)
STUDENTS(**SNumber**, Surname, FirstName, School)
EXAMS(**Student**, **Course**, Grade, Date)
where the keys are in bold. The EXAMS relation stores information of students that passed an exam for a given course .EXAMS.Student references STUDENTS.SNumber and EXAMS.Course references COURSES.Number.
We wear asked to write one SQL query that retrieves all the following information for each student number:
-their surname
-how many different exams they passed
-how many different grades they obtained
-the minimum, average and maximum grade they obtained in their exams."
Firstly, I included in my answer that I noticed that, as EXAMS only stores information about a student who passed an exam, there is no way to know if a student failed an exam and so we could only count how many different pass grades they obtained. Here is the query I wrote:
SELECT S.SNumber, S.Surame,
COUNT(E.Student) AS NumberOfExamsPassed,
COUNT(DISTINCT E.Grade) AS NumberOfDifferentPassGrades,
MIN(E.Grade) AS MinimumGrade,
MAX(E.Grade) AS MaximumGrade,
AVG(E.Grade) AS AverageGrade
FROM Students S, EXAMS E
GROUP BY E.Student;
Would this be a sufficient solution?

Answer 1

You should use Explicit Joins.
SELECT S.SNumber, S.Surame,
COUNT(E.Student) AS NumberOfExamsPassed,
COUNT(DISTINCT E.Grade) AS NumberOfDifferentPassGrades,
MIN(E.Grade) AS MinimumGrade,
MAX(E.Grade) AS MaximumGrade,
AVG(E.Grade) AS AverageGrade
FROM Students S
INNER JOIN EXAMS E ON S.SNumber = E.Student
GROUP BY E.Student;