number-of-unique-subjects-taught-by-each-teacher

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Database

Table: <code>Teacher</code>

<pre>
+-------------+------+
| 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.
</pre>

&nbsp;

Write a solution to calculate&nbsp;the number of unique subjects each teacher teaches in the university.

Return the result table in any order.

The&nbsp;result format is shown in the following example.

&nbsp;
Example 1:

<pre>
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.
</pre>