Number of Unique Subjects Taught by Each Teacher (#166)

Author: remy727

README.md

@@ -493,6 +493,7 @@
 | 1683 | Invalid Tweets | [MySQL](./database/1683-invalid-tweets.sql) | Easy |
 | 1757 | Recyclable and Low Fat Products | [MySQL](./database/1757-recyclable-and-low-fat-products.sql) | Easy |
 | 1934 | Confirmation Rate | [MySQL](./database/1934-confirmation-rate.sql) | Medium |
+| 2356 | Confirmation Rate | [MySQL](./database/2356-number-of-unique-subjects-taught-by-each-teacher.sql) | Easy |
 
 ### Shell
 | # | Title | Solution | Difficulty |

database/2356-number-of-unique-subjects-taught-by-each-teacher.sql

@@ -0,0 +1,58 @@
+-- 2356. Number of Unique Subjects Taught by Each Teacher
+-- Easy
+-- https://leetcode.com/problems/number-of-unique-subjects-taught-by-each-teacher
+
+/*
+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.
+*/
+
+SELECT
+  teacher_id, COUNT(DISTINCT subject_id) as cnt
+FROM
+  Teacher
+GROUP BY
+  teacher_id;