题解 | #找出每个学校GPA最低的同学#

# select min(gpa) from user_profile
#     group by university

# select device_id,university,gpa from user_profile
# where gpa in (select min(gpa) from user_profile
#     group by university)
# order by university

# SELECT DISTINCT (device_id,university,gpa) FROM user_profile,(SELECT MIN(gpa) min_gpa FROM user_profile
#     GROUP BY university) temp
# WHERE user_profile.gpa = temp.min_gpa
# ORDER BY university

SELECT  device_id, user_profile.university,gpa FROM user_profile,(SELECT  university,MIN(gpa) min_gpa FROM user_profile
    GROUP BY university) temp
WHERE user_profile.gpa = temp.min_gpa AND user_profile.university = temp.university
ORDER BY user_profile.university

user_profile.university = temp.university 必须要有这一句，否则当学生的gpa等于其它学校的min(gpa)时，即使这个学生不是本校的min(gpa)，他也会被认为是min(gpa)