leetcode - 580. Count Student Number in Departments

난이도 : Medium

 

Table: Student

+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| student_id   | int     |
| student_name | varchar |
| gender       | varchar |
| dept_id      | int     |
+--------------+---------+
student_id is the primary key column for this table.
dept_id is a foreign key to dept_id in the Department tables.
Each row of this table indicates the name of a student, their gender, and the id of their department.

 

Table: Department

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| dept_id     | int     |
| dept_name   | varchar |
+-------------+---------+
dept_id is the primary key column for this table.
Each row of this table contains the id and the name of a department.

 

Write an SQL query to report the respective department name and number of students majoring in each department for all departments in the Department table (even ones with no current students).

Return the result table ordered by student_number in descending order. In case of a tie, order them by dept_name alphabetically.

 

 

SELECT dept_name
     , COUNT(student_id) student_number
FROM Department
     LEFT JOIN Student ON Department.dept_id = Student.dept_id
GROUP BY dept_name
ORDER BY student_number DESC, dept_name

Accepted (5.94%)

 

 

SELECT dept_name
     , COALESCE(student_num, 0) student_number
FROM Department
     LEFT JOIN (SELECT dept_id
                     , COUNT(student_id) student_num
                FROM student
                GROUP BY dept_id) sub
          ON Department.dept_id = sub.dept_id
ORDER BY student_number DESC, Department.dept_name

Accepted (14.66%)