基本sql语句练习

红太狼 2022-05-14 00:23 275阅读 0赞

\-- 教师表  
CREATE TABLE teacher(  
    tno INT NOT NULL PRIMARY KEY,  
    tname VARCHAR(20) NOT NULL  
);

INSERT INTO teacher(tno,tname)VALUES(1,'张老师');  
INSERT INTO teacher(tno,tname)VALUES(2,'王老师');  
INSERT INTO teacher(tno,tname)VALUES(3,'李老师');  
INSERT INTO teacher(tno,tname)VALUES(4,'赵老师');  
INSERT INTO teacher(tno,tname)VALUES(5,'刘老师');  
INSERT INTO teacher(tno,tname)VALUES(6,'向老师');  
INSERT INTO teacher(tno,tname)VALUES(7,'李文静');  
INSERT INTO teacher(tno,tname)VALUES(8,'叶平');

\-- 学生表  
CREATE TABLE student(  
    sno int NOT NULL PRIMARY KEY,  
    sname varchar(20) NOT NULL,  
    sage datetime NOT NULL,  
    ssex char(2) NOT NULL  
);

INSERT INTO student(sno,sname,sage,ssex) VALUES(1,'张三','1990-1-23','男');  
INSERT INTO student(sno,sname,sage,ssex) VALUES(2,'李四','1992-12-12','男');  
INSERT INTO student(sno,sname,sage,ssex) VALUES(3,'张飒','1991-9-9','男');  
INSERT INTO student(sno,sname,sage,ssex) VALUES(4,'莉莉','1993-3-23','女');  
INSERT INTO student(sno,sname,sage,ssex) VALUES(5,'王弼','1992-6-21','男');  
INSERT INTO student(sno,sname,sage,ssex) VALUES(6,'王丽','1994-10-10','女');  
INSERT INTO student(sno,sname,sage,ssex) VALUES(7,'刘香','1990-12-22','女');

\-- 课程表  
CREATE TABLE course(  
    cno int NOT NULL PRIMARY KEY,  
    cname nvarchar(20) NOT NULL,  
    tno int NOT NULL  
);

\-- 添加外键  
ALTER TABLE course  
ADD CONSTRAINT fk\_course\_teacher  
FOREIGN KEY (tno) REFERENCES teacher (tno);

insert into course(cno,cname,tno) values(1,'企业管理',3);  
insert into course(cno,cname,tno) values(2,'马克思',1);  
insert into course(cno,cname,tno) values(3,'UML',2);  
insert into course(cno,cname,tno) values(4,'数据库',5);  
insert into course(cno,cname,tno) values(5,'物理',8);

\-- 创建成绩表  
CREATE TABLE sc(  
    sno int NOT NULL,  
    cno int NOT NULL,  
    score int NOT NULL  
);

ALTER TABLE sc  
ADD CONSTRAINT fk\_sc\_course  
FOREIGN KEY (cno) REFERENCES course (cno);

ALTER TABLE sc  
ADD CONSTRAINT fk\_sc\_student  
FOREIGN KEY (sno) REFERENCES student (sno);

INSERT INTO sc(sno,cno,score)VALUES(1,1,80);  
INSERT INTO sc(sno,cno,score)VALUES(1,2,86);  
INSERT INTO sc(sno,cno,score)VALUES(1,3,83);  
INSERT INTO sc(sno,cno,score)VALUES(1,4,89);

INSERT INTO sc(sno,cno,score)VALUES(2,1,50);  
INSERT INTO sc(sno,cno,score)VALUES(2,2,36);  
INSERT INTO sc(sno,cno,score)VALUES(2,3,43);  
INSERT INTO sc(sno,cno,score)VALUES(2,4,59);

INSERT INTO sc(sno,cno,score)VALUES(3,1,50);  
INSERT INTO sc(sno,cno,score)VALUES(3,2,96);  
INSERT INTO sc(sno,cno,score)VALUES(3,3,73);  
INSERT INTO sc(sno,cno,score)VALUES(3,4,69);

INSERT INTO sc(sno,cno,score)VALUES(4,1,90);  
INSERT INTO sc(sno,cno,score)VALUES(4,2,36);  
INSERT INTO sc(sno,cno,score)VALUES(4,3,88);  
INSERT INTO sc(sno,cno,score)VALUES(4,4,99);

INSERT INTO sc(sno,cno,score)VALUES(5,1,90);  
INSERT INTO sc(sno,cno,score)VALUES(5,2,96);  
INSERT INTO sc(sno,cno,score)VALUES(5,3,98);  
INSERT INTO sc(sno,cno,score)VALUES(5,4,99);

INSERT INTO sc(sno,cno,score)VALUES(6,1,70);  
INSERT INTO sc(sno,cno,score)VALUES(6,2,66);  
INSERT INTO sc(sno,cno,score)VALUES(6,3,58);  
INSERT INTO sc(sno,cno,score)VALUES(6,4,79);

INSERT INTO sc(sno,cno,score)VALUES(7,1,80);  
INSERT INTO sc(sno,cno,score)VALUES(7,2,76);  
INSERT INTO sc(sno,cno,score)VALUES(7,3,68);  
INSERT INTO sc(sno,cno,score)VALUES(7,4,59);

INSERT INTO sc(sno,cno,score)VALUES(7,5,89);

1、查询课程1的成绩 比 课程2的成绩 高 的所有学生的学号；

SELECT \* FROM (  
SELECT \* FROM sc WHERE cno =1)a ,(  
SELECT \* FROM sc WHERE cno =2) b WHERE a.score > b.score AND a.sno = b.sno

SELECT a.sno FROM  
(SELECT sno,score FROM sc WHERE cno=1) AS a,  
(SELECT sno,score FROM sc WHERE cno=2) AS b  
WHERE a.score>b.score AND a.sno=b.sno;

2、查询平均成绩大于60分的同学的学号和平均成绩；  
SELECT sno,AVG(score) avg FROM sc GROUP BY sno HAVING avg > 60

SELECT sno,AVG(score) AS sscore FROM sc GROUP BY sno HAVING AVG(score) >60;

3、查询所有同学的学号、姓名、选课数、总成绩；  
SELECT a.\*, b.sname FROM(  
SELECT sno, COUNT(cno) num, sum(score) score FROM sc GROUP BY sno)a, student b WHERE a.sno = b.sno

SELECT a.sno AS 学号, b.sname AS 姓名,  
COUNT(a.cno) AS 选课数, SUM(a.score) AS 总成绩  
FROM sc a, student b  
WHERE a.sno = b.sno  
GROUP BY a.sno, b.sname;

4、查询姓“李”的老师的个数；  
SELECT COUNT(\*) FROM teacher WHERE tname like '李%'

SELECT COUNT(DISTINCT(tname)) FROM teacher WHERE tname LIKE '李%';

5、查询没学过“叶平”老师课的同学的学号、姓名；  
SELECT student.sno, student.sname FROM student  
 WHERE sno NOT IN (SELECT sno FROM teacher a, course b, sc c  
WHERE a.tno = b.tno AND a.tname = '叶平' AND b.cno = c.cno)

SELECT student.sno,student.sname FROM student  
WHERE sno NOT IN (SELECT DISTINCT(sc.sno) FROM sc,course,teacher  
WHERE sc.cno=course.cno AND teacher.tno=course.tno AND teacher.tname='叶平');

6、查询同时学过课程1和课程2的同学的学号、姓名；  
SELECT sno, sname FROM student WHERE sno IN (  
SELECT sno FROM sc WHERE cno =1 )  
 AND sno IN (  
SELECT sno FROM sc WHERE cno = 2)

SELECT sno, sname FROM student  
WHERE sno IN (SELECT sno FROM sc WHERE sc.cno = 1)  
AND sno IN (SELECT sno FROM sc WHERE sc.cno = 2);

9、查询所有课程成绩小于60分的同学的学号、姓名；  
SELECT a.sno, a.sname FROM student a, (  
SELECT sno,MAX(score) max FROM sc GROUP BY sno HAVING max < 60) b WHERE a.sno = b.sno

SELECT sno, sname FROM student  
WHERE sno NOT IN (SELECT DISTINCT sno FROM sc WHERE score > 60);

10、查询所有课程成绩大于60分的同学的学号、姓名；  
SELECT sno, sname FROM student  
WHERE sno NOT IN (SELECT DISTINCT sno FROM sc WHERE score < 60);

SELECT sno,sname FROM student  
WHERE sno NOT IN (SELECT DISTINCT sno FROM sc WHERE score < 60);

11、查询没有学全所有课的同学的学号、姓名；  
SELECT sno, COUNT(cno) num FROM sc GROUP BY sno HAVING num < (SELECT COUNT(\*) FROM course)

select student.sno, student.sname  
from student, sc  
where student.sno = sc.sno  
group by student.sno, student.sname  
having count(sc.cno) < (select count(cno) from course);

12、查询至少有一门课程 与 学号为1的同学所学课程 相同的同学的学号和姓名；

SELECT DISTINCT sc.sno, student.sname FROM sc,student WHERE sc.sno = student.sno AND sc.cno     IN( SELECT cno FROM sc WHERE sno =1) AND sc.sno <> 1

select distinct a.sno, a.sname  
from student a, sc b  
where a.sno <> 1 and a.sno=b.sno and  
b.cno in (select cno from sc where sno = 1);

13、把“sc”表中“刘老师”所教课的成绩都更改为此课程的平均成绩；  
UPDATE sc SET score = ( SELECT c.\* FROM (  
SELECT avg(score) FROM sc WHERE cno = (  
SELECT cno FROM teacher a, course b WHERE a.tno = b.tno AND  a.tname='刘老师')) c)WHERE cno= (  
SELECT cno FROM teacher a, course b WHERE a.tno = b.tno AND  a.tname='刘老师')

update sc set score = (  
select avg(sc\_2.score) from sc sc\_2 where sc\_2.cno=sc.cno)  
from course,teacher where course.cno=sc.cno and course.tno=teacher.tno and teacher.tname='刘老师';

UPDATE sc SET score = (  
SELECT AVG(score) FROM sc1 GROUP BY sc1.cno  
HAVING sc1.cno = (SELECT c.cno  
     FROM course AS c, teacher AS t  
       WHERE c.tno = t.tno  
       AND t.tname = '刘老师'))  
WHERE cno IN (SELECT c.cno  
FROM course AS c, teacher AS t  
WHERE c.tno = t.tno  
AND t.tname = '刘老师');

CREATE TABLE sc1(  
    sno int NOT NULL,  
    cno int NOT NULL,  
    score int NOT NULL  
);

INSERT INTO sc1  
SELECT \*  
FROM sc;

TRUNCATE TABLE sc;

INSERT INTO sc  
SELECT \*  
FROM sc1;

14、查询和2号同学学习的课程完全相同的其他同学学号和姓名；  
SELECT a.sno, SUM(a.cno) q, AVG(a.cno) w FROM sc a,(  
SELECT sno,SUM(cno) sum,AVG(cno) avg FROM sc WHERE sno =2)b GROUP BY a.sno HAVING a.sno <> 2 AND q = b.sum and w = b.avg

select a.sno, a.sname FROM student a, sc b WHERE a.sno <> 2 AND a.sno = b.sno GROUP BY a.sno, a.sname  
HAVING SUM(cno) = (SELECT SUM(cno) FROM sc WHERE sno = 2) AND AVG(cno)= (SELECT AVG(cno) FROM sc WHERE sno = 2)

select b.sno, b.sname  
from sc a, student b  
where b.sno <> 2 and a.sno = b.sno  
group by b.sno, b.sname  
having sum(cno) = (select sum(cno) from sc where sno = 2);

15、删除学习“叶平”老师课的sc表记录；  
DELETE FROM sc WHERE cno IN (  
SELECT cno FROM(  
SELECT cno FROM teacher a,course b WHERE a.tno = b.tno AND tname = '叶平')a)

DELETE FROM sc  
WHERE cno = (SELECT c.cno  
             FROM course AS c, teacher AS t  
             WHERE c.tno = t.tno  
             AND t.tname = '叶平');

16、向sc表中插入一些记录，这些记录要求符合以下条件：  
\--将没有课程3成绩同学的该成绩补齐, 其成绩取所有学生的课程2的平均成绩；  
UPDATE sc SET score = (SELECT a FROM(  
SELECT AVG(score) a FROM sc WHERE cno=2 ) b) WHERE sno IN (SELECT sno FROM (SELECT sno FROM sc WHERE score ='' AND cno =3) c)

INSERT sc select sno, 3, (select avg(score) from sc where cno = 2)  
from student  
where sno not in (select sno from sc where cno = 3);

17、按平平均分从高到低显示所有学生的如下统计报表：  
\--学号,企业管理,马克思,UML,数据库,物理,课程数,平均分；  
SELECT sno as 学号,  
MAX(CASE WHEN cno =1 THEN score END) AS 企业管理,  
MAX(CASE WHEN cno =2 THEN score END) AS 马克思,  
MAX(CASE WHEN cno =3 THEN score END) AS UML,  
MAX(CASE WHEN cno =4 THEN score END) AS 数据库,  
MAX(CASE WHEN cno =5 THEN score END) AS 物理,  
COUNT(cno) AS 课程数,  
AVG(score) AS 平均分 FROM sc GROUP BY sno ORDER BY AVG(score) DESC

SELECT sno as 学号  
,max(case when cno = 1 then score end) AS 企业管理  
,max(case when cno = 2 then score end) AS 马克思  
,max(case when cno = 3 then score end) AS UML  
,max(case when cno = 4 then score end) AS 数据库  
,max(case when cno = 5 then score end) AS 物理  
,count(cno) AS 课程数  
,avg(score) AS 平均分  
FROM sc  
GROUP by sno  
ORDER by avg(score) DESC;

18、查询各科成绩最高分和最低分：以如下形式显示：课程号，最高分，最低分；  
SELECT cno AS 课程号, MAX(score) AS 最高分, MIN(score) AS 最低分 FROM sc GROUP BY cno

select cno as 课程号, max(score) as 最高分, min(score) 最低分  
from sc group by cno;

19、查询课程号、课程名、各科平均成绩、及格率，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 max(a.cno),max(b.cname),AVG(score),100 \* SUM(CASE WHEN ifnull(score,0)>=60 THEN 1 ELSE 0 END)/count(score) FROM sc a, course b WHERE a.cno = b.cno GROUP BY a.cno,cname

SELECT max(t.cno) AS 课程号,  
max(course.cname) AS 课程名,  
ifnull(AVG(score),0) AS 平均成绩,  
100 \* SUM(CASE WHEN ifnull(score,0)>=60 THEN 1 ELSE 0 END)/count(score) AS 及格率  
FROM sc t, course  
where t.cno = course.cno  
GROUP BY t.cno  
ORDER BY 平均成绩 asc, 及格率 desc;

20、查询如下课程平均成绩和及格率的百分数(用"1行"显示): 企业管理（001），马克思（002），UML （003），数据库（004）；  
SELECT AVG(CASE WHEN cno = 1 THEN score END),  
AVG(CASE WHEN cno = 2 THEN score END),  
AVG(CASE WHEN cno = 3 THEN score END),  
AVG(CASE WHEN cno = 4 THEN score END),  
100 \* SUM(CASE WHEN cno = 1 AND IFNULL(score,0) >= 60 THEN 1 ELSE 0 END) / SUM(CASE WHEN cno = 1 THEN 1 ELSE 0 END),  
100 \* SUM(CASE WHEN cno = 2 AND IFNULL(score,0) >= 60 THEN 1 ELSE 0 END) / SUM(CASE WHEN cno = 2 THEN 1 ELSE 0 END),  
100 \* SUM(CASE WHEN cno = 3 AND IFNULL(score,0) >= 60 THEN 1 ELSE 0 END) / SUM(CASE WHEN cno = 3 THEN 1 ELSE 0 END),  
100 \* SUM(CASE WHEN cno = 4 AND IFNULL(score,0) >= 60 THEN 1 ELSE 0 END) / SUM(CASE WHEN cno = 4 THEN 1 ELSE 0 END)  
FROM sc

select  
avg(case when cno = 1 then score end) as 平均分1,    
avg(case when cno = 2 then score end) as 平均分2,  
avg(case when cno = 3 then score end) as 平均分3,  
avg(case when cno = 4 then score end) as 平均分4,  
100 \* sum(case when cno = 1 and score > 60 then 1 else 0 end) / sum(case when cno = 1 then 1 else 0 end) as 及格率1,  
100 \* sum(case when cno = 2 and score > 60 then 1 else 0 end) / sum(case when cno = 2 then 1 else 0 end) as 及格率2,  
100 \* sum(case when cno = 3 and score > 60 then 1 else 0 end) / sum(case when cno = 3 then 1 else 0 end) as 及格率3,  
100 \* sum(case when cno = 4 and score > 60 then 1 else 0 end) / sum(case when cno = 4 then 1 else 0 end) as 及格率4  
from sc

21、查询不同老师所教不同课程平均分, 从高到低显示  
\--张老师 数据库 88；  
SELECT a.tname, b.cname, AVG(c.score) FROM teacher a, course b, sc c WHERE a.tno = b.tno AND b.cno = c.cno GROUP BY c.cno ORDER BY AVG(c.score) DESC

select max(c.tname) as 教师, max(b.cname) 课程, avg(a.score) 平均分  
from sc a, course b, teacher c  
where a.cno = b.cno and b.tno = c.tno  
group by a.cno  
order by 平均分 desc;

22、查询如下课程成绩均在第3名到第6名之间的学生的成绩：  
\--\[学生ID\],\[学生姓名\],企业管理,马克思,UML,数据库,平均成绩；  
SELECT MAX(a.sno) 学号, MAX(b.sname) 姓名,  
MAX(CASE WHEN cno =1 THEN score END) 企业管理,  
MAX(CASE WHEN cno = 2 THEN score END) 马克思,  
MAX(CASE WHEN cno = 3 THEN score END) UML,  
MAX(CASE WHEN cno = 4 THEN score END) 数据库,  
AVG(score) 平均分  
FROM sc a, student b  
WHERE a.sno IN (SELECT sno FROM (SELECT sno FROM sc WHERE cno = 1 ORDER BY score desc LIMIT 2, 4) a1)  
AND a.sno IN (SELECT sno FROM (SELECT sno FROM sc WHERE cno = 2 ORDER BY score desc LIMIT 2, 4) a2)  
AND a.sno IN (SELECT sno FROM (SELECT sno FROM sc WHERE cno = 3 ORDER BY score desc LIMIT 2, 4) a3)  
AND a.sno IN (SELECT sno FROM (SELECT sno FROM sc WHERE cno = 4 ORDER BY score desc LIMIT 2, 4) a4)  
AND a.sno = b.sno  
GROUP BY a.sno;

select max(a.sno) 学号, max(b.sname) 姓名,  
max(case when cno = 1 then score end) as 企业管理,  
max(case when cno = 2 then score end) as 马克思,  
max(case when cno = 3 then score end) as UML,  
max(case when cno = 4 then score end) as 数据库,  
avg(score) as 平均分  
from sc a, student b  
where a.sno in (select sno from (select sno from sc where cno = 1 order by score desc limit 2, 4) as in1)  
  and a.sno in (select sno from (select sno from sc where cno = 2 order by score desc limit 2, 4) as in2)  
  and a.sno in (select sno from (select sno from sc where cno = 3 order by score desc limit 2, 4) as in3)  
  and a.sno in (select sno from (select sno from sc where cno = 4 order by score desc limit 2, 4) as in4)  
  and a.sno = b.sno  
group by a.sno;

23、统计打印各科成绩,各分数段人数:课程ID,课程名称,\[100-85\],\[85-70\],\[70-60\],\[ <60\]；  
SELECT MAX(a.cno) 课程ID, MAX(b.cname) 课程名称,  
MAX(CASE WHEN score >= 85 then 1 else 0 END) '\[100-85\]',  
MAX(CASE WHEN score < 85 AND score >=70 THEN 1 ELSE 0 END) '\[85-70\]',  
MAX(CASE WHEN score < 70 AND score >= 60 then 1 ELSE 0 END) '\[70-60\]',  
MAX(CASE WHEN score < 60 THEN 1 ELSE 0 END) '\[ <60\]'  
FROM sc a, course b WHERE a.cno = b.cno  
GROUP BY a.cno

select sc.cno as 课程ID, cname as 课程名称,  
sum(case when score >= 85 then 1 else 0 end) as '\[100-85\]',  
sum(case when score < 85 and score >= 70 then 1 else 0 end) as '\[85-70\]',  
sum(case when score < 70 and score >= 60 then 1 else 0 end) as '\[70-60\]',  
sum(case when score < 60 then 1 else 0 end) as '\[ <60\]'  
from sc, course  
where sc.cno = course.cno  
group by sc.cno, cname;

24、查询学生平均分及其名次；  
SELECT sno, AVG(score) FROM sc GROUP BY sno ORDER BY AVG(score) DESC

SELECT (@i:=@i+1) 名次,  
sno 学号,  
avg 平均成绩  
FROM (  
    SELECT sno, AVG(score) avg FROM sc GROUP BY sno ORDER BY AVG(score) DESC) a,  
(SELECT @i:=0) i;

SELECT drug\_productor,@y:=@y+1 as num FROM( SELECT drug\_productor FROM ts\_drug a GROUP BY drug\_productor) c,(SELECT @y:=0) d

SELECT 1+(SELECT COUNT(DISTINCT 平均成绩)  
  FROM (SELECT sno, AVG(score) AS 平均成绩 FROM sc GROUP BY sno) AS T1  
      WHERE T1.平均成绩 > T2.平均成绩) AS 名次,  
sno AS 学生学号, T2.平均成绩 AS 平均成绩  
FROM (SELECT sno, AVG(score) AS 平均成绩 FROM sc GROUP BY sno) AS T2  
ORDER BY 平均成绩 desc;

25、查询各科成绩前三名的记录:(不考虑成绩并列情况)；  
(SELECT '1' 课程,sno 学号,MAX(CASE WHEN cno = 1 THEN score END) '成绩' FROM sc GROUP BY sno ORDER BY 成绩 DESC LIMIT 0, 3 )  
UNION  
(SELECT '2' 课程,sno 学号,MAX(CASE WHEN cno = 2 THEN score END) '成绩' FROM sc GROUP BY sno ORDER BY 成绩 DESC LIMIT 0, 3 )  
UNION  
(SELECT '3' 课程,sno 学号,MAX(CASE WHEN cno = 3 THEN score END) '成绩' FROM sc GROUP BY sno ORDER BY 成绩 DESC LIMIT 0, 3 )  
UNION  
(SELECT '4' 课程,sno 学号,MAX(CASE WHEN cno = 4 THEN score END) '成绩' FROM sc GROUP BY sno ORDER BY 成绩 DESC LIMIT 0, 3 )

SELECT a.cno, a.sno, a.score  
FROM sc AS a  
WHERE (SELECT COUNT(cno) FROM sc WHERE cno = a.cno AND a.score < score) <= 2  
ORDER BY a.cno ASC, a.score DESC;

26、查询每门课程被选修的学生数；  
SELECT cname, COUNT(sno) FROM course a, sc b WHERE a.cno = b.cno GROUP BY b.cno

select cno,count(sno) from sc group by cno;

27、查查询出只选修了一门课程的全部学生的学号和姓名；  
SELECT a.sno, a.sname FROM student a,sc b WHERE a.sno = b.sno GROUP BY b.sno HAVING COUNT(cno)=1  
   
SELECT sc.sno, student.sname, count(cno) AS 选课数  
FROM sc, student  
WHERE sc.sno = student.sno  
GROUP BY sc.sno, student.sname  
HAVING count(cno) = 1;

28、查询男生、女生人数；  
SELECT SUM(CASE WHEN ssex='男' THEN 1 ELSE 0 END) '男生',  
SUM(CASE WHEN ssex='女' THEN 1 ELSE 0 END) '女生' FROM student

select  
(select count(1) from student where ssex = '男') 男生人数,  
(select count(1) from student where ssex = '女') 女生人数;

29、查询姓“张”的学生名单；  
SELECT \* FROM student WHERE sname LIKE '张%'

SELECT sname FROM 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(\*) sum FROM student GROUP BY sname,ssex HAVING sum > 1

select sname,count(\*) from student group by sname having count(\*)>1;

31、1991年出生的学生名单(注：student表中sage列的类型是datetime)；  
SELECT \* FROM student WHERE sage LIKE '1991%'

SELECT sno, sname  
FROM student  
WHERE Year(sage) = 1991;

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 cno 课程号, AVG(score) 平均成绩 FROM sc GROUP BY cno ORDER BY 平均成绩 ASC, 课程号 DESC

select cno 课程号, avg(score) 平均分  
from sc group by cno order by 平均分 asc, cno desc;

33、查询平均成绩大于80的所有学生的学号、姓名和平均成绩；  
SELECT a.sno, a.sname, AVG(b.score) FROM student a, sc b WHERE a.sno = b.sno GROUP BY b.sno HAVING AVG(b.score) > 80

select  
s1.sno,  
s.sname,  
AVG(s1.score) as '平均成绩'  
from student s,sc s1  
where s.sno=s1.sno  
group by s1.sno,s.sname  
having AVG(s1.score)>80;

34、查询 数据库 分数 低于60的学生姓名和分数；  
SELECT a.sname, b.score FROM student a, sc b WHERE b.score < 60 AND a.sno = b.sno AND b.cno=(  
    SELECT cno FROM course WHERE cname='数据库')

select c.sname, a.score  
from sc a, course b, student c  
where a.cno = b.cno and a.sno = c.sno  
 and b.cname = '数据库' and score < 60;

35、查询所有学生的选课情况；  
\--学号，姓名，课程，课号  
SELECT a.sno, a.sname, b.cno, b.cname FROM student a, course b, sc c WHERE a.sno = c.sno AND b.cno = c.cno ORDER BY sno,cno

SELECT sc.sno 学号,sname 姓名,cname 课程, sc.cno 课号  
FROM sc,student,course  
WHERE sc.sno=student.sno and sc.cno=course.cno  
ORDER BY sc.sno

36、查询成绩在70分以上的学生姓名、课程名称和分数；  
SELECT a.sname, b.cname, c.score FROM student a, course b, sc c WHERE c.score > 70 AND a.sno = c.sno AND b.cno = c.cno

select  
s.sname,  
c.cname,  
(s1.score) as '分数'  
from student s,sc s1,course c  
where s.sno=s1.sno  and c.cno=s1.cno and s1.score>70;

37、查询不及格的课程，并按课程号从大到小排列；  
SELECT DISTINCT cno FROM sc WHERE score < 60 ORDER BY cno DESC

select  
sc.cno  
,c.cname  
,sc.score  
from sc ,course c  
where sc.score<60 and c.cno=sc.cno  
order by sc.cno desc;

38、查询课程编号为3且课程成绩在80分以上的学生的学号和姓名；  
SELECT a.sno, a.sname FROM student a, sc b WHERE a.sno = b.sno AND cno = 3 AND score > 80

select sc.sno,student.sname from sc,student where sc.sno=student.sno and score>80 and cno=3;

39、求选了课程的学生人数；  
SELECT COUNT(DISTINCT sno) FROM sc

select count(distinct sno) from sc;

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 a.sname, b.score  
FROM student a, sc b, course c, teacher d  
WHERE a.sno = b.sno  
AND b.cno = c.cno  
AND c.tno = d.tno  
AND d.tname = '叶平'  
ORDER BY b.score DESC LIMIT 0, 1

select student.sname,cname, score  
from student,sc,course C,teacher  
where student.sno=sc.sno and sc.cno=C.cno and C.tno=teacher.tno  
and teacher.tname ='叶平'  
and sc.score=(select max(score) from sc where cno = C.cno);

41、查询各个课程及相应的选修人数；  
SELECT cname 课程名, COUNT(sno) 选修人数  
FROM course a, sc b  
WHERE a.cno = b.cno  
GROUP BY a.cname

select cno 课程号, count(1) 选修人数 from sc group by cno;

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 a.sno, a.cno, a.score FROM sc a, sc b  
WHERE a.score = b.score  
AND a.cno <> b.cno

select distinct A.sno, A.cno,B.score  
from sc A ,sc B  
where A.Score=B.Score and A.cno <>B.cno  
order by B.score;

43、查询每门课程成绩最好的前两名的学生ID；  
SELECT a.cno, a.sno, a.score  
FROM sc a  
WHERE (SELECT COUNT(\*) FROM sc b WHERE a.cno = b.cno AND a.score < b.score ) <=1  
ORDER BY a.cno ,a.score DESC

SELECT a.cno, a.sno, a.score  
FROM sc AS a  
WHERE (SELECT COUNT(cno) FROM sc WHERE cno = a.cno AND a.score < score) <= 1  
ORDER BY a.cno ASC, a.score DESC;

44、统计每门课程的学生选修人数(至少有2人选修的课程才统计)。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 cno, COUNT(sno) 选修人数 FROM sc GROUP BY cno HAVING 选修人数 >= 2 ORDER BY  选修人数 DESC, cno ASC

select cno as 课程号,count(1) as 人数  
from sc  
group by cno having count(1) > 1  
order by count(1) desc,cno;

45、检索至少选修了5门课程的学生学号；  
SELECT DISTINCT sno, COUNT(cno) FROM sc GROUP BY sno HAVING COUNT(cno) >= 5

select sno from sc group by sno having count(1) >= 5;

46、查询全部学生都选修的课程的课程号和课程名；  
SELECT a.cno, a.cname FROM course a, sc b  
WHERE a.cno = b.cno  
GROUP BY b.cno  
HAVING COUNT(sno) = (SELECT COUNT(\*) FROM student)

select course.cno, cname  
from sc, course  
where sc.cno = course.cno  
group by course.cno, cname  
having count(sc.cno) = (select count(1) from student);

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 student WHERE sno NOT IN (  
SELECT sno FROM sc WHERE cno IN (  
SELECT cno FROM course WHERE tno IN (  
SELECT tno FROM teacher WHERE tname = '叶平')))

select sno, sname from student  
where sno not in(  
    select sno from sc where cno in  
    (select a.cno from course a, teacher b where a.tno = b.tno and b.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 sno, AVG(score), COUNT(cno)  
FROM sc  
WHERE score < 60  
GROUP BY sno  
HAVING COUNT(cno) > 1

select sno 学号, avg(score) 平均分, count(1) 不及格课程数  
from sc where score < 60 group by sno having count(1) > 2;

49、检索4号课程分数大于60的同学学号，按分数降序排列；  
SELECT sno, score FROM sc WHERE cno = 4 AND score > 60 ORDER BY score DESC

select sno, score from sc where cno = 4 and score > 60 order by score desc;

50、删除2号同学的课程1的成绩；  
DELETE FROM sc WHERE sno = 2 AND cno = 1

51、查询成绩最好的课程；  
SELECT a.cno, a.cname, AVG(score)  
FROM course a, sc b  
WHERE a.cno = b.cno  
GROUP BY b.cno  
ORDER BY AVG(score) DESC  
LIMIT 1

SELECT sc.cno 课程号, c.cname 课程名称, AVG(score) 平均分  
FROM sc, course c  
WHERE sc.cno = c.cno  
GROUP BY sc.cno  
ORDER BY AVG(score) DESC  
LIMIT 1;

52、查询最受欢迎的老师(选修学生最多的老师)；  
SELECT tname,COUNT(sno) FROM sc a, course b, teacher c  
WHERE a.cno = b.cno  
AND b.tno = c.tno  
GROUP BY c.tname  
ORDER BY COUNT(sno) DESC

SELECT t.tname 老师, c.cname 课程名, COUNT(sno) 选课人数  
FROM sc, course c, teacher t  
WHERE sc.cno = c.cno  
AND c.tno = t.tno  
GROUP BY sc.cno  
ORDER BY COUNT(sno) DESC  
LIMIT 1;

53、查询需要补考的各科学生清单；  
SELECT a.sno, a.sname, b.cno, b.cname, c.score  
FROM student a, course b, sc c  
WHERE a.sno = c.cno  
AND b.cno = c.cno  
AND c.score < 60

SELECT c.cname 课程, s.sno 学生ID, s.sname 学生名, score 成绩  
FROM sc, course c, student s  
WHERE sc.cno = c.cno  
AND sc.sno = s.sno  
AND score < 60  
ORDER BY 课程, 学生ID;

参考：

[https://blog.csdn.net/oliver\_wq/article/details/78374439][https_blog.csdn.net_oliver_wq_article_details_78374439]

[https_blog.csdn.net_oliver_wq_article_details_78374439]: https://blog.csdn.net/oliver_wq/article/details/78374439