select device_id, gender, age, gpa from user_profile where university = '山东大学' union all select device_id, gender, age, gpa from user_profile where gender = 'male'
union会去重,使用union all不会去重,保留两个子查询所有结果
select device_id, gender, age, gpa from user_profile where university = '山东大学' union all select device_id, gender, age, gpa from user_profile where gender = 'male'
union会去重,使用union all不会去重,保留两个子查询所有结果