leetcode : 2356. Number of Unique Subjects Taught by Each Teacher

leetcode : 2356. Number of Unique Subjects Taught by Each Teacher

• [leetcode : 2356. Number of Unique Subjects Taught by Each Teacher]

---

다이어그램

erDiagram
    Teacher {
        teacher_id int PK
        subject_id int
        dept_id int
    }

• 각 선생 별 과목 수 구하기

---

문제 풀이

MySQL 1

SELECT teacher_id, COUNT(DISTINCT subject_id) as cnt
FROM teacher
GROUP BY teacher_id

• GRUOP BY + COUNT DISTINCT

---

MySQL 2

SELECT
    TEACHER_ID as teacher_id,
    COUNT(DISTINCT SUBJECT_ID) as cnt
FROM TEACHER
GROUP BY TEACHER_ID

• GRUOP BY + COUNT DISTINCT
• 대소문자좀 구별하지마라 좀!!

---

Pandas

def count_unique_subjects(teacher: pd.DataFrame) -> pd.DataFrame:
    grouped = teacher.groupby('teacher_id').agg(
        cnt = ('subject_id','nunique')
    ).reset_index()
    return grouped

• groupby + unique

---

Pandas

def count_unique_subjects(teacher: pd.DataFrame) -> pd.DataFrame:
    grouped = teacher.groupby('teacher_id').nunique().reset_index().rename(columns={'subject_id':'cnt'})
    return grouped[['teacher_id','cnt']]

• 한 컬럼에만 집계를 해주는거라 agg 대신 nunique를 사용해서 풀이.

---

코멘트

• 기본문제