MySQL query select rows from table according to specific key that is not in another table

Question

How to select all exams by its ID and title (from table 'exams'), that a student (in table 'grades') hasn't written yet?

TABLE: grades

+--------------+----+----
|student_number|e_id| ...
+--------------+----+----
|888075        |1   | ...
|888075        |2   | ...
|888075        |4   | ...
|637020        |2   | ...
+--------------+----+----

TABLE: exams

+----+------+
|e_id|title |
+----+------+
|1   |exam 1|
|2   |exam 2|
|3   |exam 3|
|4   |exam 4|
+----+------+

In this particular case I would expect the following output for student 888075 :

+--+------+
|id|title |
+--+------+
|3 |exam 3|
+--+------+

I just need the inverse selection of this:

SELECT e.e_id as id, e.title as title
FROM grades g
LEFT JOIN exams e
ON g.e_id = e.e_id
WHERE g.student_number = '888075'

Answer 1

Your query was close -- just reverse the joins and check for null accordingly:

SELECT e.e_id as id, e.title as title
FROM exams e
   LEFT JOIN grades g ON g.e_id = e.e_id
      AND g.student_number = '888075'
WHERE g.e_id IS NULL

Answer 2

You need to select those e_id that are not in e_id 's that student participated.

SELECT aa.e_id AS id, aa.title
FROM exams AS aa
WHERE e_id NOT IN (
    SELECT e_id
    FROM grades
    WHERE student_number = '888075'
    GROUP BY e_id
);

OR

SELECT aa.e_id AS id, aa.title
FROM exams AS aa
WHERE e_id NOT IN (
    SELECT DISTINCT e_id
    FROM grades
    WHERE student_number = '888075'
);

OR

SELECT aa.e_id AS id, aa.title 
FROM exams AS aa 
WHERE NOT EXISTS (
    SELECT e_id 
    FROM grades AS bb
    WHERE aa.e_id = bb.e_id AND bb.student_number = '888075'
);