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.
#

# Write your MySQL query statement below

SELECT teacher_id, COUNT(DISTINCT subject_id) AS cnt
FROM Teacher
GROUP BY teacher_id;