小编use*_*199的帖子

select 
    disease_name 
from 
    disease 
where 
    disease_id=
    (select disease_id from disease_symptom where
        disease.disease_id=disease_symptom.disease_id AND 
        symptom_id=
               (select symptom_id from symptom where symptom.symptom_id=disease_symptom.symptom_id
                AND symptom_name='fever' OR symptom_name='head ache'))

给出子查询返回多行的错误.原因是什么？