MySQL经典50道题全部标准答案，个人的宝贵建议和方法分享等【诗书画唱】
1.查询“某1”课程比“某2”课程成绩高的所有学生的学号；
select a.sid from (select sid,score from SC where cid=1) a,(select sid,score from SC where cid=2) b where a.score>b.score and a.sid=b.sid;
2.查询平均成绩大于60分的同学的学号和平均成绩；
select sid,AVG(score) from SC group by sid having avg(score) > 60;
3.查询所有同学的学号、姓名、选课数、总成绩
select Student.sid,Student.sname,count(SC.cid),sum(SC.score) from Student left join SC on Student.sid=SC.sid group by sid,sname;
4.查询姓“李”的老师的个数；
select count(Teacher.tid) from Teacher where Teacher.tname like '李%';
5.查询没学过“张三”老师课的同学的学号、姓名；
select s.sid,s.sname from Student as s where sid not in(select DISTINCT(s.sid) from Course as c,SC as s,Teacher as t where c.cid=s.cid AND c.tid=t.tid AND t.tname='张三');
6.查询学过“```”并且也学过编号“```”课程的同学的学号、姓名；
select a.sid,a.sname from
(select s.sid,s.sname from Student as s,Course as c,SC as sc where c.cname='数学' AND s.sid=sc.sid AND c.cid=sc.cid) a,
(select s.sid,s.sname from Student as s,Course as c,SC as sc where c.cname='语文' AND s.sid=sc.sid AND c.cid=sc.cid) b
WHERE a.sid=b.sid;
7.查询学过“张三”老师所教的所有课的同学的学号、姓名；
SELECT a.sid,a.sname from (select s.sid,s.sname from Student as s,Course as c,SC as sc ,Teacher as t where t.tname='王五' AND s.sid=sc.sid AND c.cid=sc.cid AND c.tid=t.tid) a;
8.查询课程编号“01”的成绩比课程编号“02”课程低的所有同学的学号、姓名；
SELECT DISTINCT(a.sid),a.sname from (select sc.score,s.sid,s.sname from Student as s,SC as sc where sc.cid=01) a, (select sc.score,s.sid,s.sname from Student as s,SC as sc where sc.cid=02) b where a.score<b.score AND a.sid=b.sid;
9.查询所有课程成绩小于60分的同学的学号、姓名；
select s.sid,s.sname,sc.cid from Student as s,SC as sc where sc.score<60 AND sc.sid=s.sid;
10.查询没有学全所有课的同学的学号、姓名；
select s.sid,s.sname from Student as s,SC as sc where s.sid=sc.sid GROUP BY s.sid,s.sname HAVING count(sc.cid)<(select count(cid) from Course);
11.查询至少有一门课与学号为“01”的同学所学相同的同学的学号和姓名；
SELECT Student.sid,Student.sname FROM SC,Student WHERE EXISTS (
SELECT cid FROM SC WHERE sid=01 AND SC.cid=cid
) AND Student.sid=SC.sid GROUP BY Student.sid,Student.sname;
12.查询和"01"号的同学学习的课程完全相同的其他同学的学号和姓名
select * from Student where sid in (
SELECT sid FROM SC WHERE
cid in (SELECT cid FROM SC WHERE sid=01) AND sid!=01 GROUP BY sid HAVING COUNT(*)=(SELECT COUNT(*) FROM SC WHERE sid=01)
)
13.把“SC”表中“张三”老师教的课的成绩都更改为此课程的平均成绩；
update SC,(
SELECT t.tid,avg(score) as ascore
from Course as c,SC as sc,Teacher as t
WHERE t.tname='张三' AND c.tid=t.tid AND c.cid=sc.cid
)a set score=a.ascore
;
14、查询没学过"张三"老师讲授的任一门课程的学生姓名
SELECT * FROM Student WHERE sid in(
SELECT sid FROM SC WHERE cid NOT in(
SELECT cid
FROM Teacher,Course WHERE Teacher.tname='张三' AND Teacher.tid=Course.tid
)
)
15、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩
SELECT s.sid,s.sname,AVG(score)
FROM SC sc JOIN Student s on sc.sid=s.sid WHERE
sc.score<60 GROUP BY s.sid,s.sname HAVING COUNT(sc.score)>=2
16、检索"01"课程分数小于60，按分数降序排列的学生信息
SELECT Student.*,SC.score from Student,SC WHERE EXISTS (
SELECT sid,score FROM SC WHERE cid=01 AND score<60 AND sid=Student.sid
) AND Student.sid=SC.sid AND SC.cid=01 ORDER BY SC.score DESC;
17、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩
SELECT a.*
,SUM(CASE WHEN b.cid='01' THEN b.score ELSE 0 END) AS s01
,SUM(CASE WHEN b.cid='02' THEN b.score ELSE 0 END) AS s02
,SUM(CASE WHEN b.cid='03' THEN b.score ELSE 0 END) AS s03
,AVG(CASE WHEN b.score IS NULL THEN 0 ELSE b.score END) avs
FROM Student a
LEFT JOIN SC b
ON a.sid=b.sid
GROUP BY 1,2,3,4
ORDER BY avs DESC;
18.查询各科成绩最高分、最低分和平均分：以如下形式显示：课程ID，课程name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率
SELECT a.cid
,a.cname
,MAX(b.score)
,MIN(b.score)
,AVG(b.score)
,SUM(CASE WHEN b.score>=60 THEN 1 ELSE 0 END)/COUNT(1)
,SUM(CASE WHEN b.score>=70 AND b.score<80 THEN 1 ELSE 0 END)/COUNT(1)
,SUM(CASE WHEN b.score>=80 AND b.score<90 THEN 1 ELSE 0 END)/COUNT(1)
,SUM(CASE WHEN b.score>=90 THEN 1 ELSE 0 END)/COUNT(1)
FROM Course a
INNER JOIN SC b
ON a.cid=b.cid
GROUP BY 1,2;
19.按各科平均成绩从低到高和及格率的百分数从高到低顺序
SELECT cid,avg_score,CONCAT(de,'%') 及格率
FROM(
SELECT sc0.cid,
AVG(sc0.score) avg_score,
CAST((
SELECT COUNT(1) FROM SC WHERE cid=sc0.cid AND score>=60
)*1.0/(
SELECT COUNT(1) FROM SC WHERE cid=sc0.cid
)*100 AS DECIMAL(10,2)) de
FROM SC sc0
GROUP BY sc0.cid
ORDER BY avg_score,de DESC)a;
20、查询学生的总成绩并进行排名
select a.sid,a.sname,a.sage,a.sum,count(b.sum) rank
from
(select a.sid,
a.sname,
a.sage,
a.ssex,
sum(b.score) sum
from student a inner join sc b
on a.sid=b.sid
group by a.sid,
a.sname,
a.sage,
a.ssex) a left join
(select a.sid,
a.sname,
a.sage,
a.ssex,
sum(b.score) sum
from student a inner join sc b
on a.sid=b.sid
group by a.sid,
a.sname,
a.sage,
a.ssex) b
on 1=1
where b.sum>a.sum
group by a.sid,a.sname,a.sage,a.sum order by rank;
21、查询不同老师所教不同课程平均分从高到低显示
SELECT Course.tid,Teacher.tname,a.cid,a.avg_score
FROM (SELECT cid,avg(score) avg_score FROM SC GROUP BY cid ) a,Course,Teacher
WHERE a.cid=Course.cid AND Teacher.tid=Course.tid ORDER BY a.avg_score DESC;
22、查询所有课程的成绩第2名到第3名的学生信息及该课程成绩
SELECT s.*,sc0.*
FROM SC sc0 INNER JOIN Student s ON s.sid=sc0.sid
WHERE (SELECT COUNT(DISTINCT score) FROM SC WHERE sc0.cid=SC.cid AND sc0.score>SC.score) BETWEEN 2 AND 3
ORDER BY sc0.cid;
23、统计各科成绩各分数段人数：课程编号,课程名称,[100-85],[85-70],[70-60],[0-60]及所占百分比
这道题 太复杂了懒的写
SELECT cid,count(SELECT score FROM SC WHERE score BETWEEN 85 AND 100) a,count(SELECT score FROM SC WHERE score BETWEEN 85 AND 100)/count(score),count(score) FROM SC GROUP BY cid;
SELECT count(1) FROM (SELECT score FROM SC WHERE score BETWEEN 85 AND 100)a;
24、查询学生平均成绩及其名次
SELECT a.sid,
a.avg_score,
sum(case when a.avg_score<b.avg_score then 1 else 0 end)+1 scc
FROM (SELECT sid,avg(score) avg_score FROM SC GROUP BY sid) a INNER JOIN
(SELECT sid,avg(score) avg_score FROM SC GROUP BY sid) b
GROUP BY a.sid,
a.avg_score
ORDER BY scc;
25、查询各科成绩前三名的记录
SELECT sc0.*,
(SELECT count(1) FROM SC WHERE SC.cid=sc0.cid AND SC.score>sc0.score)+1 rank
FROM SC sc0
GROUP BY 2,1,3
HAVING rank<=3
ORDER BY sc0.cid,rank;
26.查询每门课程被选修的学生数
SELECT sc.cid,count(sc.sid) from Course c,SC sc WHERE c.cid=sc.cid GROUP BY sc.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 s.sid,s.sname from SC as sc,Student AS s WHERE sc.sid=s.sid GROUP BY sc.sid,s.sname HAVING COUNT(cid)=2;
28、查询男生、女生人数
SELECT count(ssex='女'),count(ssex='男') FROM Student;
29、查询名字中含有"风"字的学生信息
SELECT Student.* FROM Student WHERE sname like '%风%';
30、查询同名同性学生名单，并统计同名人数
SELECT sname,ssex,count(1)
FROM Student GROUP BY 1,2
HAVING count(1)>1;
31、查询1990年出生的学生名单(注：Student表中Sage列的类型是datetime)
SELECT Student.* FROM Student WHERE YEAR(sage)=1990;
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(score) from SC GROUP BY cid order by avg(score),cid DESC;
37.查询不及格的课程，并按课程号从大到小排列
SELECT cid,score FROM SC WHERE score<60 order by cid DESC;
38.查询课程编号为"01"且课程成绩在60分以上的学生的学号和姓名；
SELECT s.sid,s.sname,score,sc.cid
FROM SC as sc,Student as s
WHERE sc.sid=s.sid AND sc.cid=01 AND score>60;
40.查询选修“张三”老师所授课程的学生中，成绩最高的学生姓名及其成绩
这道题写的时候想出了两种方达，都能实现
SELECT *
FROM (SELECT s.sid as aid,s.sname as aname,sc.score as ascore,t.tname FROM SC as sc,Student s,Course as c,Teacher as t
WHERE sc.sid=s.sid AND c.cid=sc.cid AND c.tid=t.tid AND t.tname="张三" ORDER BY score) a LIMIT 0,1;
SELECT s.sid,s.sname,a.ascore
FROM SC as sc,Student s,Course as c,Teacher as t ,
(SELECT MAX(score) ascore FROM SC as sc,Student s,Course as c,Teacher as t
WHERE sc.sid=s.sid AND c.cid=sc.cid AND c.tid=t.tid AND t.tname="张三" ) a
WHERE sc.sid=s.sid AND c.cid=sc.cid AND c.tid=t.tid AND t.tname="张三" AND sc.score=a.ascore;
42、查询每门功课成绩最好的前两名
SELECT sc.* FROM SC sc WHERE (SELECT COUNT(1) FROM SC WHERE SC.cid=sc.cid AND score>sc.score)<2 ORDER BY sc.cid,sc.score;
43、统计每门课程的学生选修人数（超过5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，若人数相同，按课程号升序排列
SELECT cid,count(1) count
FROM SC GROUP BY cid HAVING count(1)>=5 ORDER BY count desc,cid ;
44、检索至少选修两门课程的学生学号
SELECT a.*,b.count
FROM Student a INNER JOIN (SELECT sid,count(cid) count FROM SC GROUP BY sid HAVING count>1)b
ON a.sid=b.sid GROUP BY 1,2,3,4;
45、查询选修了全部课程的学生信息
SELECT sid,count(cid) count_c FROM SC
GROUP BY sid
HAVING count_c=(SELECT COUNT(1) FROM Course);
46、查询各学生的年龄
SELECT Student.*,YEAR(CURDATE())-YEAR(Student.sage) FROM Student;
47、查询本周过生日的学生
SELECT * FROM Student WHERE WEEKOFYEAR(NOW())-WEEKOFYEAR(sage)=0;
48、查询下周过生日的学生
SELECT * FROM Student WHERE WEEKOFYEAR(NOW())-WEEKOFYEAR(sage)=-1;
49、查询本月过生日的学生
SELECT * FROM Student WHERE MONTH(NOW())-MONTH(sage)=0;
50、查询下月过生日的学生
SELECT * FROM Student WHERE MONTH(NOW())-MONTH(sage)=-1;
