@@ -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