一道数据库面试题，大家帮忙看看！

[疯狂的指针]

数据库中存在一个表A(课程标识为bid，分数为score)，请写出查询语句，求出该表中每门课程中分数在70到80分之间的人数占本门课程全部人数的比例！

[charlie_coolp]

select bid, sum(case when score >= 70 and score <= 80 then 1 else 0 end) / count(score) percent from a group by bid

[碧水幽幽泉]

楼主，你所说的70到80分之间是指70~80，还是70-79？

1.70~79
select  bid,round(sum(case when score >= 70 and score < 80 then 0)/count(*)*100,2)||'%'  percent from A group by bid

2.70~79
select  bid,round(sum(case when score >= 70 and score < 80 then 0)/count(*)*100,2)||'%'  percent from A group by bid

[碧水幽幽泉]

2.70~80
select  bid,round(sum(case when score >= 70 and score <= 80 then 0)/count(*)*100,2)||'%'  percent from A group by bid

[碧水幽幽泉]

1.70~79
select bid,round(sum(case when score >= 70 and score < 80 then 0)/count(*)*100,2)||'%'  percent 
  from A 
group by bid;
 
2.70~80
select bid,round(sum(case when score >= 70 and score <= 80 then 0)/count(*)*100,2)||'%'  percent 
  from A 
group by bid

[疯狂的指针]

引用 4 楼 碧水幽幽泉的回复:

1.70~79
select bid,round(sum(case when score >= 70 and score < 80 then 0)/count(*)*100,2)||'%'  percent 
  from A 
group by bid;
 
2.70~80
select bid,round(sum(case when score >= 70 and score <= 80 then 0)/count(*)*100,2)||'%'  percent 
  from A 
group by bid

大于等于70，小于等于80，谢谢你的解答，受教了！