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2356. Number of Unique Subjects Taught by Each Teacher

SQL 50 · Sorting and Grouping (day 4). Decode it with the hints, solve it on LeetCode, then compare with the reference solution in MySQLPostgreSQL.

Your work

Status Notes Your solution (MySQLPostgreSQL)

Open one at a time. Try to finish with as few as you can.

1. What does one output row represent?

One teacher.

2. Approach

GROUP BY teacher_id, COUNT(DISTINCT subject_id).

3. The trap

The same subject in two departments counts once.

Tested on MySQL 8.0 and PostgreSQL 16. Switch dialect at the top of the page.

Show the MySQLPostgreSQL solution

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