[프로그래머스] 연도 별 평균 미세먼지 농도 조회하기

문제

제출

SELECT YEAR(ym) as YEAR,round(avg(pm_val1),2) as 'PM10',round(avg(pm_val2),2) as 'PM2.5'
from air_pollution
where location1='경기도' and location2='수원'
group by 1
order by 1 asc

🚨 error

SELECT date_format(ym,'%Y') as YEAR,round(avg(pm_val1),2) as 'PM10',round(avg(pm_val2),2) as 'PM2.5'
from air_pollution
where location1='경기도' and location2='수원'
group by 1
order by 1 asc

YEAR(ym) vs DATE_FORMAT(ym, '%Y')

• YEAR(ym) 은 정수(INT) 타입을 반환
• DATE_FORMAT(ym, '%Y') 은 문자열(VARCHAR) 타입을 반환
  → GROUP BY에서 에러날 가능성 있음
  → ONLY_FULL_GROUP_BY 모드가 활성화된 경우, 명확한 데이터 타입 일치가 필요함.