技術標籤：mysql統計各部門人數統計不及格人數pta

表資訊

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]所佔百分比

然而這麼寫是不對的~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;
 

要這麼寫

select score.c_id,c_name,
sum(case when 0<score and score<= 60 then 1 else 0 end)/count(score) 不及格率, 
sum(case when 60<score and score<= 70 then 1 else 0 end)/count(score) 中等率, 
sum(case when 70<score and score<=85 then 1 else 0 end)/count(score) 優良率, 
sum(case when 85<score and score<=100 then 1 else 0 end)/count(score) 優秀率 
from score left join course on score.c_id = course.c_id
group by score.c_id;