I used a sub query that is resulting wrong output when submitted but correct as tested :-(

#1

select distinct reviewer_name from reviewers where reviewer_id = (select reviewer_id from ratings where reviewer_stars = NULL);

I used a sub query that is resulting wrong output when submitted but correct as tested… I already tried IS NULL that also results in error : ERROR 1242 (21000) at line 39: Subquery returns more than 1 row

#2

correct:-
select distinct reviewer_name from reviewers where reviewer_id in (select reviewer_id from ratings where reviewer_stars is NULL);

#3

reviewer_id is a single value but the subquery returns list of reviewer_ids hence may be tested correct for some case but it is not completely corrrect.