EASY

Author: evanmathew

2356. Number of Unique Subjects Taught by Each Teacher.sql

@@ -1,3 +1,64 @@
+-- Problem:
+
+/*
+Table: Teacher
+
++-------------+------+
+| Column Name | Type |
++-------------+------+
+| teacher_id  | int  |
+| subject_id  | int  |
+| dept_id     | int  |
++-------------+------+
+(subject_id, dept_id) is the primary key (combinations of columns with unique values) of this table.
+Each row in this table indicates that the teacher with teacher_id teaches the subject subject_id in the department dept_id.
+ 
+
+Write a solution to calculate the number of unique subjects each teacher teaches in the university.
+
+Return the result table in any order.
+
+The result format is shown in the following example.
+
+ 
+
+Example 1:
+
+Input: 
+Teacher table:
++------------+------------+---------+
+| teacher_id | subject_id | dept_id |
++------------+------------+---------+
+| 1          | 2          | 3       |
+| 1          | 2          | 4       |
+| 1          | 3          | 3       |
+| 2          | 1          | 1       |
+| 2          | 2          | 1       |
+| 2          | 3          | 1       |
+| 2          | 4          | 1       |
++------------+------------+---------+
+Output:  
++------------+-----+
+| teacher_id | cnt |
++------------+-----+
+| 1          | 2   |
+| 2          | 4   |
++------------+-----+
+Explanation: 
+Teacher 1:
+  - They teach subject 2 in departments 3 and 4.
+  - They teach subject 3 in department 3.
+Teacher 2:
+  - They teach subject 1 in department 1.
+  - They teach subject 2 in department 1.
+  - They teach subject 3 in department 1.
+  - They teach subject 4 in department 1.
+*/
+
+-------------------------------------------------------------------------------
+
+-- Solution:
+
 SELECT teacher_id, COUNT(DISTINCT subject_id) AS cnt FROM Teacher
 GROUP BY teacher_id
 ORDER BY teacher_id