sid as 学生学号,

avggrade

FROM (

SELECT sid,AVG(grade )as avggrade FROM t_score GROUP BY sid

) AS T2

ORDER BY avggrade desc;

25、查询各科成绩前三名的记录:(不考虑成绩并列情况)
SELECT t1.sid as 学生ID,t1.cid as 课程ID,grade as 分数

FROM t_score t1 WHERE grade IN (

SELECT TOP 3 grade FROM t_score t2 WHERE t1.cid = t2.cid ORDER BY grade DESC

)

ORDER BY t1.cid;
26、查询每门课程被选修的学生数
select cid,count(sid) from t_score group by cid;
27、查询出只选修了一门课程的全部学生的学号和姓名
select t1.sid,t2.sname,count(t1.cid) AS 选课数 from t_score t1,t_student t2

where t1.sid=t2.sid

group by t1.sid ,t2.sname

having count(t1.cid)=1;
28、查询男生、女生人数
Select count(ssex) as 男生人数 from t_student group by ssex having ssex='男';

Select count(ssex) as 女生人数 from t_student group by ssex having ssex='女';
29、查询姓“张”的学生名单
SELECT sname FROM t_student WHERE sname like '张%';
30、查询同名同性学生名单，并统计同名人数
select sname,count(*) from t-student group by sname having count(*)>1;
31、1981年出生的学生名单(注：Student表中Sage列的类型是datetime)
select sname, CONVERT(char(11),DATEPART(year,sage)) as age

from t_tudent

where CONVERT(char(11),DATEPART(year,Sage))='1981';
32、查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列
Select cid,Avg(grade ) from t_score group by cid order by Avg(grade ),cid DESC

33、查询平均成绩大于85的所有学生的学号、姓名和平均成绩
select t1.sname, t2.sid ,avg(t2.grade ) from t_student t1, t_score t2

where t1.sid=t2.sid group by t2.sid,t1.sname

having avg(t2.grade )>85;
34、查询课程名称为“数据库”，且分数低于60的学生姓名和分数
Select t1.sname,isnull(t2.grade ,0) from t_student t1, t_score t2,t_course t3

where t2.sid = t1.sid and t2.cid = t3.cid

and t3.cname='数据库'and t2.grade <60;
35、查询所有学生的选课情况；
SELECT t1.sid, t1.cid,t2.sname,t3.cname FROM t_score t1,t_student t2,t_course t3

where t1.sid = t2.sid and t1.cid = t3.cid ;
36、查询任何一门课程成绩在70分以上的姓名、课程名称和分数；
SELECT distinct t1.sid,t1.sname,t2.cid, t2.grade FROM t_student t1, t_score t2

WHERE t2.grade >=70 AND t2.sid = t1.sid;
37、查询不及格的课程，并按课程号从大到小排列
select cid from t_score where grade < 60 order by cid ;
38、查询课程编号为003且课程成绩在80分以上的学生的学号和姓名；
select t1.sid,t2.sname from t_score t1,t_student t2

where t1.sid = t2.sid and t1.grade > 80 and t1.cid = '003';
39、求选了课程的学生人数
select count(*) from t_score;
40、查询选修“叶平”老师所授课程的学生中，成绩最高的学生姓名及其成绩
select t1.sname,t2.grade from t_student t1, t_score t2,t_course t3,t_teacher t4

where t1.sid = t2.sid

and t2.cid = t3.cid

and t3.tid = t4.tid

and t4.Tname = '叶平'

and t2.grade = (select max(grade )from t_score where cid=t3.cid );
41、查询各个课程及相应的选修人数
select count(*) from t_score group by cid
42、查询不同课程成绩相同的学生的学号、课程号、学生成绩
select distinct t1.sid,t2.grade from t_score t1 , t_score t2

where t1.grade = t2.grade and t1.cid <>t2.cid ;
43、查询每门功成绩最好的前两名
SELECT t1.sid as 学生ID,t1.cid as 课程ID,grade as 分数 FROM t_score t1

WHERE grade IN (

SELECT TOP 2 grade FROM t_score

WHERE t1.cid = cid ORDER BY grade DESC

)

ORDER BY t1.cid;
44、统计每门课程的学生选修人数（超过10人的课程才统计）。要求输出课程号和选修人数，查询结果按人数降序排列，查询结果按人数降序排列，若人数相同，按课程号升序排列
select cid as 课程号,count(*) as 人数 from t_score

group by cid

order by count(*) desc,cid
45、检索至少选修两门课程的学生学号
select sid from t_score group by sid having count(*) > = 2
46、查询全部学生都选修的课程的课程号和课程名
select cid,cname from t_course where cid in (select cid from t_score group by cid)
47、查询没学过“叶平”老师讲授的任一门课程的学生姓名
select sname from t_student

where sid not in (

select sid from t_course t1,t_teacher t2, t_score t3

where t1.tid = t2.tid

and t3.cid =t 1.cid

and t2.tname = '叶平'

);
48、查询两门以上不及格课程的同学的学号及其平均成绩
select sid,avg(isnull(grade ,0)) from t_score

where sid in (