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