refactor 1280

Author: fishercoder1534

database/_1280.sql

@@ -1,104 +1,3 @@
---1280. Students and Examinations
---
---Table: Students
---
---+---------------+---------+
---| Column Name   | Type    |
---+---------------+---------+
---| student_id    | int     |
---| student_name  | varchar |
---+---------------+---------+
---student_id is the primary key 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 for this table.
---Each row of this table contains a name of one subject in the school.
---
---
---Table: Examinations
---
---+--------------+---------+
---| Column Name  | Type    |
---+--------------+---------+
---| student_id   | int     |
---| subject_name | varchar |
---+--------------+---------+
---There is no primary key for this table. It may contain duplicates.
---Each student from Students table takes every course from Subjects table.
---Each row of this table indicates that a student with ID student_id attended the exam of subject_name.
---
---
---Write an SQL query to find the number of times each student attended each exam.
---
---Order the result table by student_id and subject_name.
---
---The query result format is in the following example:
---
---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         |
---+------------+--------------+
---Result table:
---+------------+--------------+--------------+----------------+
---| 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              |
---+------------+--------------+--------------+----------------+
---The result table should contain all students and all subjects.
---Alice attended Math exam 3 times, Physics exam 2 times and Programming exam 1 time.
---Bob attended Math exam 1 time, Programming exam 1 time and didn't attend the Physics exam.
---Alex didn't attend any exam.
---John attended Math exam 1 time, Physics exam 1 time and Programming exam 1 time.
-
-
 select a.student_id, a.student_name, b.subject_name, count(c.subject_name) as attended_exams
 from Students as a
 join Subjects as b