Table: Students
+---------------+---------+ +| Column Name | Type | ++---------------+---------+ +| student_id | int | +| student_name | varchar | ++---------------+---------+ +student_id is the primary key (column with unique values) for this table. +Each row of this table contains the ID and the name of one student in the school. ++ +
+ +
Table: Subjects
+--------------+---------+ +| Column Name | Type | ++--------------+---------+ +| subject_name | varchar | ++--------------+---------+ +subject_name is the primary key (column with unique values) for this table. +Each row of this table contains the name of one subject in the school. ++ +
+ +
Table: Examinations
+--------------+---------+ +| Column Name | Type | ++--------------+---------+ +| student_id | int | +| subject_name | varchar | ++--------------+---------+ +There is no primary key (column with unique values) for this table. It may contain duplicates. +Each student from the Students table takes every course from the Subjects table. +Each row of this table indicates that a student with ID student_id attended the exam of subject_name. ++ +
+ +
Write a solution to find the number of times each student attended each exam.
+ +Return the result table ordered by student_id and subject_name.
The result format is in the following example.
+ ++
Example 1:
+ +Input: +Students table: ++------------+--------------+ +| student_id | student_name | ++------------+--------------+ +| 1 | Alice | +| 2 | Bob | +| 13 | John | +| 6 | Alex | ++------------+--------------+ +Subjects table: ++--------------+ +| subject_name | ++--------------+ +| Math | +| Physics | +| Programming | ++--------------+ +Examinations table: ++------------+--------------+ +| student_id | subject_name | ++------------+--------------+ +| 1 | Math | +| 1 | Physics | +| 1 | Programming | +| 2 | Programming | +| 1 | Physics | +| 1 | Math | +| 13 | Math | +| 13 | Programming | +| 13 | Physics | +| 2 | Math | +| 1 | Math | ++------------+--------------+ +Output: ++------------+--------------+--------------+----------------+ +| student_id | student_name | subject_name | attended_exams | ++------------+--------------+--------------+----------------+ +| 1 | Alice | Math | 3 | +| 1 | Alice | Physics | 2 | +| 1 | Alice | Programming | 1 | +| 2 | Bob | Math | 1 | +| 2 | Bob | Physics | 0 | +| 2 | Bob | Programming | 1 | +| 6 | Alex | Math | 0 | +| 6 | Alex | Physics | 0 | +| 6 | Alex | Programming | 0 | +| 13 | John | Math | 1 | +| 13 | John | Physics | 1 | +| 13 | John | Programming | 1 | ++------------+--------------+--------------+----------------+ +Explanation: +The result table should contain all students and all subjects. +Alice attended the Math exam 3 times, the Physics exam 2 times, and the Programming exam 1 time. +Bob attended the Math exam 1 time, the Programming exam 1 time, and did not attend the Physics exam. +Alex did not attend any exams. +John attended the Math exam 1 time, the Physics exam 1 time, and the Programming exam 1 time. ++