LeetCode-in-Java
2356. Number of Unique Subjects Taught by Each Teacher
Easy
SQL Schema
Table: Teacher
+-------------+------+
| Column Name | Type |
+-------------+------+
| teacher_id | int |
| subject_id | int |
| dept_id | int |
+-------------+------+
(subject_id, dept_id) is the primary key for 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 an SQL query to report the number of unique subjects each teacher teaches in the university.
Return the result table in any order.
The query 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
# Write your MySQL query statement below
select teacher_id, count(distinct subject_id) as "cnt"
from Teacher
group by teacher_id