ifnull() 함수 사용법

IFNULL

해당 Column의 값이 NULL을 반환할 때, 다른 값으로 출력할 수 있도록 하는 함수이다.

-- count,min,max,avg에 NULL값이 있으면 0으로 변경해준다.
select rv.first_name,rv.last_name,count(r.rating) as COUNT ,
ifnull(min(r.rating),0) as MIN,  
ifnull(max(r.rating),0) as MAX, 
ifnull(avg(r.rating),0) as AVG,
if( count(r.rating) = 0, 'INACTIVE','ACTIVE') as STATUS
from reviewers rv
left join reviews r
	on rv.id = r.reviewer_id 
group by rv.id;