表信息

成績表score

課程表course

-- 統計各科成績各分數段人數：課程編號,課程名稱,(0-60],(60,70],(70,85],(85,100]所占百分比

然而這么寫是不對的~between and 是兩邊閉區間

select score.c_id,c_name,

sum(score between 0 and 60)/count(score) 不及格率,

sum(score between 60 and 70) 中等率,

sum(score between 70 and 85)/count(score) 優良率,

sum(score between 85 and 100)/count(score) 優秀率

from score left join course on score.c_id = course.c_id

group by score.c_id;

要這么寫

select score.c_id,c_name,

sum(case when 0

sum(case when 60

sum(case when 70

sum(case when 85

from score left join course on score.c_id = course.c_id

group by score.c_id;

總結

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