[SQL] 중복 제거하기

문제링크

https://school.programmers.co.kr/learn/courses/30/lessons/59408

프로그래머스

1. 핵심

• COUNT
  • ROW의 개수를 세기
• DISTINCT
  • 이름 중복 제거 → "중복 제거" → DISTINCT로 중복 제거

2. 코드(MySQL)

SELECT COUNT(DISTINCT NAME) AS COUNT 
FROM ANIMAL_INS
WHERE NAME IS NOT NULL;

3. 활용예제

STUDENT_ID	NAME	DEPARTMENT	GRADE
1	John	Computer	A
2	Alice	Mathematics	B
3	Bob	Computer	C
4	Alice	Mathematics	B
5	John	Computer	A

SELECT DEPARTMENT, COUNT(DISTINCT NAME) AS UNIQUE_STUDENTS_COUNT
FROM STUDENT
GROUP BY DEPARTMENT;

DEPARTMENT	UNIQUE STUDENTS COUNT
Computer	2
Mathematics	1