一、删除除了学号字段以外，其它字段都相同的冗余记录，只保留一条！(也就是要删除凤姐和田七中一条重复数据只留一条)

要求结果数据：

原始数据：

CREATE TABLEtbl_students (

idint NOT NULL,

namevarchar(10) DEFAULT NULL,

saxvarchar(10) DEFAULT NULL,

ageint(6) DEFAULT NULL,PRIMARY KEY(id)

) engine=InnoDB default charset=utf8;

insert into tbl_students (id, name, sax, age) values('2','李四','男','21');insert into tbl_students (id, name, sax, age) values('3','张三','女','17');insert into tbl_students (id, name, sax, age) values('4','李四','男','12');insert into tbl_students (id, name, sax, age) values('6','凤姐','女','20');insert into tbl_students (id, name, sax, age) values('5','凤姐','女','20');insert into tbl_students (id, name, sax, age) values('7','田七','男','18');insert into tbl_students (id, name, sax, age) values('1','田七','男','18');insert into tbl_students (id, name, sax, age) values('8','张三','男','17');

答案：

delete fromtbl_studentswhere id not in (select id from (select min(id) id from tbl_students group by name,sax,age) t );

注意：一定要需要临时表，否则删除表时与统计的表为一张表，将抛出异常

二、查询各科成绩都及格的学员

(要求查询出参加考试的各科成绩都高于60分，不管参加了多少科考试)

要求结果：

表：

CREATE TABLEtbl_score (

idint NOT NULL,

usernamevarchar(20) DEFAULT NULL,

coursevarchar(20) DEFAULT NULL,

scoreint DEFAULT NULL,PRIMARY KEY(id)

) engine=InnoDB default charset=utf8;

数据：

insert into tbl_score (id, username, course, score) values('1','张三','语文','50');insert into tbl_score (id, username, course, score) values('2','张三','数学','80');insert into tbl_score (id, username, course, score) values('3','张三','英语','90');insert into tbl_score (id, username, course, score) values('4','李四','语文','70');insert into tbl_score (id, username, course, score) values('5','李四','数学','80');insert into tbl_score (id, username, course, score) values('6','李四','英语','80');insert into tbl_score (id, username, course, score) values('7','王五','语文','50');insert into tbl_score (id, username, course, score) values('8','王五','英语','70');insert into tbl_score (id, username, course, score) values('9','赵六','数学','90');

答案：

select username,score from tbl_score where id not in (select id from tbl_score where score < 60)

表(MYSQL)：Student(sid,Sname,Sage,Ssex) 学生表

CREATE TABLEstudent (

sidvarchar(10) NOT NULL,

sNamevarchar(20) DEFAULT NULL,

sAgedatetime DEFAULT '1980-10-12 23:12:36',

sSexvarchar(10) DEFAULT NULL,PRIMARY KEY(sid)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Course(cid,Cname,tid) 课程表

CREATE TABLEcourse (

cidvarchar(10) NOT NULL,

cNamevarchar(10) DEFAULT NULL,

tidint(20) DEFAULT NULL,PRIMARY KEY(cid)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

SC(sid,cid,score) 成绩表

CREATE TABLEsc (

idvarchar(10) NOT NULL,

sidvarchar(10) DEFAULT NULL,

cidvarchar(10) DEFAULT NULL,

scoreint(10) DEFAULT NULL,PRIMARY KEY(id)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Teacher(tid,Tname) 教师表

CREATE TABLEtaacher (

tidint(10) DEFAULT NULL,

tNamevarchar(10) DEFAULT NULL,

PRIMARY KEY(tid)) ENGINE=InnoDB DEFAULT CHARSET=utf8;

数据：(MySQL)

insert into taacher(tid,tName) values (1,'李老师'),(2,'何以琛'),(3,'叶平');INSERT INTO `student` VALUES ('1', '张三丰', '1980-10-12 23:12:36', '男');INSERT INTO `student` VALUES ('2', '张无极', '1995-10-12 23:12:36', '男');INSERT INTO `student` VALUES ('3', '李奎', '1992-10-12 23:12:36', '女');INSERT INTO `student` VALUES ('4', '李元宝', '1980-10-12 23:12:36', '女');INSERT INTO `student` VALUES ('5', '李世明', '1981-10-12 23:12:36', '男');INSERT INTO `student` VALUES ('6', '赵六', '1986-10-12 23:12:36', '男');INSERT INTO `student` VALUES ('7', '田七', '1981-10-12 23:12:36', '女');insert into sc(id,sid,cid,score) values (1,'1','001',80),(2,'1','002',60),(3,'1','003',75),(4,'2','001',85),(5,'2','002',70),(6,'3','004',100),(7,'3','001',90),(8,'3','002',55),(9,'4','002',65),(10,'4','003',60);insert into course(cid,cName,tid) values ('001','企业管理',3),('002','马克思',3),('003','UML',2),('004','数据库',1),('005','英语',1);

SQL问题：

1.查询“001”课程比“002”课程成绩高的所有学生的学号;

select a.sid ,a.cid,a.score,b.sid,b.cid,b.score from (select cid,sid,score from sc where cid='001') a,

(select cid,sid,score from sc where cid='002') bwhere 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) as avgscore from sc group by sid having avgscore>60;

3、查询所有同学的学号、姓名、选课数、总成绩;

select s.sid,s.sname, count(sc.cid) as countcourse,sum(sc.score) as sumscore fromstudent sleft join sc on sc.sid=s.sidgroup by s.sid,s.sname

4、查询姓“李”的老师的个数;

select count(distinct(tname)) from taacher where tname like '李%';

5、查询没学过“叶平”老师课的同学的学号、姓名;

select s.sid,s.sname fromstudent swhere sid not in(select distinct(sc.sid) fromsc,course,taacherwhere sc.cid=course.cid and taacher.tid=course.tid and taacher.tname='叶平')

6、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名;

select s.sid,s.sname fromstudent s, scwhere s.sid=sc.sid and sc.cid='001' and

exists(select * from sc s2 where s2.sid=sc.sid and s2.cid='002')

7、查询学过“叶平”老师所教的所有课的同学的学号、姓名;

select s.sid,s.sname fromstudent swhere sid in(select distinct(sc.sid) fromsc,course,taacherwhere sc.cid=course.cid and taacher.tid=course.tid and taacher.tname='叶平')

select sid,Sname

from Student

where sid in (select sid from SC ,Course ,Teacher where SC.cid=Course.cid and Teacher.tid=Course.tid and Teacher.Tname='叶平' group by sid having count(SC.cid)=(select count(cid) from Course,Teacher where Teacher.tid=Course.tid and Tname='叶平'));

8、查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名;

1>

select x.sid,x.sname from(select s.sid,s.sname,score,(select score from sc s2 where s2.sid=s.sid and s2.cid='002') asscore2fromstudent s,scwhere s.sid=sc.sid and cid='001') xwhere x.score2

2>

select s.sid,s.sname fromstudent s,

(select sid,score from sc where cid='001') sc1,

(select sid,score from sc where cid='002') sc2where sc1.sid=sc2.sid and s.sid=sc2.sid and sc2.score

9、查询所有课程成绩小于60分的同学的学号、姓名;

select sid,sname fromstudentwhere sid not in(select sid from sc where sc.score>60)

10、查询没有学全所有课的同学的学号、姓名;

1>

select s.sid,s.sname fromstudent s,scwhere s.sid=sc.sidgroup bys.sid,s.snamehaving count(cid)

2>

select s.sid,s.sname fromstudent s,

(select sid,count(cid) as countcid from sc group by sc.sid having countcid < (select count(distinct(cid)) fromcourse)) twhere s.sid=t.sid

11、查询至少有一门课与学号为“1”的同学所学相同的同学的学号和姓名;

select distinct student.sid,sname fromstudent, scwhere student.sid=sc.sid and sc.cid in (select cid from sc where sid=1)

13、把“SC”表中“叶平”老师教的课的成绩都更改为此课程的平均成绩;

updatesc,

(select c.cid,avg(score) as avgs fromsc,course c,taacher twhere sc.cid=c.cid and c.tid=t.tid and t.tname='叶平' group byc.cid) sc2set sc.score=sc2.avgs where sc.cid=sc2.cid;

14、查询和“2”号的同学学习的课程完全相同的其他同学学号和姓名;

select sid from sc wherecidin (select cid from sc where sid='1002')group bysidhaving count(*)=(select count(*) from sc where sid=2);

15、删除学习“叶平”老师课的SC表记录;

delete from sc where cid in (select DISTINCT c.cid fromcourse cleft join taacher t on t.tid=c.tidwhere t.tName='叶平');

17、按平均成绩从高到低显示所有学生的“数据库”、“企业管理”、“英语”三门的课程成绩，按如下形式显示： 学生ID,,数据库,企业管理,英语,有效课程数,有效平均分

select s.sid,avg(s.score) as avgscore,count(s.cid) ascountcourse

,(select score from sc where sc.sid=s.sid and sc.cid='001') as 'sql',(select score from sc where sc.sid=s.sid and sc.cid='002') as 'java',(select score from sc where sc.sid=s.sid and sc.cid='003') as 'python'

from sc s group by sid order by avgscore desc

18、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分

select cid "课程ID",max(score) "最高分",min(score) "最低分" from sc group by cid

19、按各科平均成绩从低到高和及格率的百分数从高到低排序

select sc.cid '课程编号', c.cName '课程名称',avg(sc.score) as '平均分', 100 * sum(if(sc.score>60, 1, 0))/count(sc.score) '及格百分比'

fromsc, course cwhere sc.cid=c.cidgroup by sc.cid order by avg(sc.score);

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)，OO&UML (003)，数据库(004)

多行显示：

select sc.cid,course.cName, avg(score) as avgscore, sum(score) fromscleft join course on sc.cid=course.cidgroup by sc.cid,course.cid order by avgscore

单行

select sum(case when cid='001' then score else 0 end)/sum(case sc.cid when '001' then 1 else 0 end) as '企业管理平均分',100 * sum(case when cid='001' and score > 60 then 1 else 0 end)/sum(case cid when '001' then 1 else 0 end) as '企业管理及格百分比'

from sc

21、查询不同老师所教不同课程平均分从高到低显示 要求显示：教师ID,教师姓名，课程ID,课程名称，平均成绩

SELECT MAX(t.tid) "教师ID",MAX(t.tName) "教师姓名",c.cid "课程ID", MAX(c.cName) "课程名称" ,AVG(sc.score) "平均成绩"

select max(t.tid) as 'teacher id',max(t.tName) as 'teacher name',

c.cidas 'course id', max(c.cName) as 'course name', avg(s.score) asavgscorefromsc s,course c,taacher twhere s.cid=c.cid and c.tid=t.tidgroup byc.tid,c.cidorder by avgscore;

23、统计各科成绩,各分数段人数:课程ID,课程名称,[100-85],[85-70],[70-60],[ <60]

select sc.cid as '课程id', c.cName as '课程名称',sum(case when sc.score between 85 and 100 then 1 else 0 end) as '85-100分人数',sum(case when sc.score between 70 and 85 then 1 else 0 end) as '70-85数',sum(case when sc.score between 60 and 70 then 1 else 0 end) as '60-70分人数',sum(case when sc.score < 60 then 1 else 0 end) as '60分以下人数'

fromsc, course cwhere sc.cid=c.cidgroup by sc.cid,c.cName;

26、查询每门课程被选修的学生数

select cid,count(distinct(sid)) as counts from sc 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 s.sid,sd.sName,count(distinct(cid)) ascountsfrom sc s,student sd where s.sid=sd.sidgroup by s.sid,sd.sName having counts=1;

28、查询男生、女生人数

select sSex,count(sSex) from student group by sSex having sSex='男';

select sSex,count(sSex) as '女生人数' from student group by sSex having sSex='女';

29、查询姓“张”的学生名单

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,sSex ,COUNT(*) FROM student GROUP BY sName,sSex HAVING COUNT(*) > 1

31、1981年出生的学生名单(注：Student表中Sage列的类型是datetime)

Mysql>

select Sname, CONVERT(char (11),DATEPART(year,Sage)) as age

from student

where CONVERT(char(11),DATEPART(year,Sage))='1981';

Oracle>

select* fromstudent wheresubstr(to_char(sage,'yyyy-MM-dd'),1,4)= '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(score) from sc group by cid order by Avg(score),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 sName,sc.sid ,avg(score) fromstudent,scwhere student.sid=sc.sid group by sc.sid,sName having avg(score)>75;

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 sd.sName,ifnull(score, 0) fromstudent sd,sc,course cwhere sc.sid=sd.sid and sc.cid=c.cid and c.cName='马克思'and score <80;

35、查询所有学生的选课情况;

selectsc.sid,sc.cid,sName,cNamefrom sc,student,course where sc.sid=student.sid and sc.cid=course.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 student.sid,student.Sname,SC.cid,SC.score

FROM student,Sc

WHERE SC.score>=70 AND SC.sid=student.sid;

37、查询不及格的课程，并按课程号从大到小排列

select cid from sc where scor e <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 SC.sid,Student.Sname from SC,Student where SC.sid=Student.sid and Score>80 and cid='003';

39、求选了课程的学生人数

select count(*) 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 Student.Sname,score

from Student,SC,Course C,Teacher

where Student.sid=SC.sid and SC.cid=C.cid and C.tid=Teacher.tid and Teacher.Tname='叶平' and SC.score=(select max(score)from SC where cid=C.cid );

41、查询各个课程及相应的选修人数

select count(*) from sc 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 A.sid,B.score from SC A ,SC B where A.Score=B.Score and A.cid <>B.cid ;

43、查询每门功课成绩最好的前两名

SELECT *

FROM sc t1

WHERE (

SELECT COUNT(*)

FROM sc t2

WHERE t1.cid=t2.cid

AND t2.score>=t1.score

) <=2 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，若人数相同，按课程号升序排列

SELECT cid "课程号",COUNT(*) "选修人数" FROM sc GROUP BY cid HAVING COUNT(*) >10 ORDER BY COUNT(*) DESC,cid

45、检索至少选修两门课程的学生学号

select sid

from sc

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 s.sName,c.cName, COUNT(*) FROM student s,course c, sc WHERE s.sid = sc.sid AND sc.cid = c.cid GROUP BY sc.cid HAVING COUNT(*) = (SELECT COUNT(*) 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 DISTINCT Sname FROM Student WHERE sid NOT IN (SELECT sid FROM Course,Teacher,SC WHERE Course.tid=Teacher.tid AND SC.cid=course.cid AND 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(ifnull(score,0)) from SC where sid in (select sid from SC where score <60 group by sid having count(*)>2)group by sid;

49、检索“004”课程分数小于60，按分数降序排列的同学学号

select sid from SC where cid='004'and score <60 order by score desc;

50、删除“1002”同学的“001”课程的成绩

delete from Sc where sid='1002' and cid='001';

行转列

CREATE TABLE stu_score (

grade_id varchar(10) DEFAULT NULL,

subject_name varchar(10) DEFAULT NULL,

max_score int(10) DEFAULT NULL

)

insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('1','语文',98);

insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('2','数学',95);

insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('2','政治',87);

insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('5','语文',97);

insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('5','数学',100);

insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('5','政治',92);

1.查询出要求的结果格式

SELECT

CASE grade_id WHEN 1 THEN '一年级'

WHEN 2 THEN '二年级'

WHEN 5 THEN '五年级'

END AS '年级',

CASE subject_name WHEN '语文' THEN max_score END AS '语文',

CASE subject_name WHEN '数学' THEN max_score END AS '数学',

CASE subject_name WHEN '政治' THEN max_score END AS '政治'

FROM stu_score

2,去除null

SELECT

CASE grade_id WHEN 1 THEN '一年级'

WHEN 2 THEN '二年级'

WHEN 5 THEN '五年级'

END AS '年级',

IFNULL(CASE subject_name WHEN '语文' THEN max_score END,0)AS '语文',

IFNULL(CASE subject_name WHEN '数学' THEN max_score END,0) AS '数学',

IFNULL(CASE subject_name WHEN '政治' THEN max_score END,0) AS '政治'

FROM stu_score

3.合并结果。

SELECT

CASE grade_id WHEN 1 THEN '一年级'

WHEN 2 THEN '二年级'

WHEN 5 THEN '五年级'

END AS '年级',

MAX(IFNULL(CASE subject_name WHEN '语文' THEN max_score END,0)) AS '语文',

MAX(IFNULL(CASE subject_name WHEN '数学' THEN max_score END,0)) AS '数学',

MAX(IFNULL(CASE subject_name WHEN '政治' THEN max_score END,0)) AS '政治'

FROM stu_score

GROUP BY grade_id

有A(id,sex,par,c1,c2),B(id,age,c1,c2)两张表，其中A.id与B.id关联，现在要求写出一条SQL语句，将B中age>50的记录的c1,c2更新到A表中同一记录中的c1,c2字段中

考点分析

这道题主要考察的是MySQL的关联UPDATE语句

延伸考点：

MySQL的关联查询语句

MySQL的关联UPDATE语句

针对刚才这道题，答案可以是如下两种形式的写法：

UPDATE A,B SET A.c1 = B.c1, A.c2 = B.c2 WHERE A.id = B.id

UPDATE A INNER JOIN B ON A.id=B.id SET A.c1 = B.c1,A.c2=B.c2

再加上B中age>50的条件：

UPDATE A,B set A.c1 = B.c1, A.c2 = B.c2 WHERE A.id = B.id and B.age > 50;

UPDATE A INNER JOIN B ON A.id = B.id set A.c1 = B.c1,A.c2 = B.c2 WHERE B.age > 50

MySQL的关联查询语句

六种关联查询

交叉连接(CROSS JOIN)

内连接(INNER JOIN)

外连接(LEFT JOIN/RIGHT JOIN)

联合查询(UNION与UNION ALL)

全连接(FULL JOIN)

交叉连接(CROSS JOIN)

SELECT * FROM A,B(,C)或者

SELECT * FROM A CROSS JOIN B (CROSS JOIN C)

没有任何关联条件，结果是笛卡尔积，结果集会很大，没有意义，很少使用

内连接(INNER JOIN)

SELECT * FROM A,B WHERE A.id=B.id或者

SELECT * FROM A INNER JOIN B ON A.id=B.id

多表中同时符合某种条件的数据记录的集合，INNER JOIN可以缩写为JOIN

内连接分为三类

等值连接：ON A.id=B.id

不等值连接：ON A.id > B.id

自连接：SELECT * FROM A T1 INNER JOIN A T2 ON T1.id=T2.pid

外连接(LEFT JOIN/RIGHT JOIN)

左外连接：LEFT OUTER JOIN, 以左表为主，先查询出左表，按照ON后的关联条件匹配右表，没有匹配到的用NULL填充，可以简写成LEFT JOIN

右外连接：RIGHT OUTER JOIN, 以右表为主，先查询出右表，按照ON后的关联条件匹配左表，没有匹配到的用NULL填充，可以简写成RIGHT JOIN

LEFT JOIN，RIGHT JOIN，INNER JOIN的区别?

联合查询(UNION与UNION ALL)

SELECT * FROM A UNION SELECT * FROM B UNION ...

就是把多个结果集集中在一起，UNION前的结果为基准，需要注意的是联合查询的列数要相等，相同的记录行会合并

如果使用UNION ALL，不会合并重复的记录行

效率 UNION 高于 UNION ALL

全连接(FULL JOIN)

MySQL不支持全连接

可以使用LEFT JOIN 和UNION和RIGHT JOIN联合使用

SELECT * FROM A LEFT JOIN B ON A.id=B.id UNION

SELECT * FROM A RIGHT JOIN B ON A.id=B.id

嵌套查询

用一条SQL语句得结果作为另外一条SQL语句得条件，效率不好把握

SELECT * FROM A WHERE id IN (SELECT id FROM B)

解题方法

根据考题要搞清楚表的结果和多表之间的关系，根据想要的结果思考使用那种关联方式，通常把要查询的列先写出来，然后分析这些列都属于哪些表，才考虑使用关联查询

真题

问题1：

为了记录足球比赛的结果，设计表如下：

team：参赛队伍表

match：赛程表

其中，match赛程表中的hostTeamID与guestTeamID都和team表中的teamID关联，查询2006-6-1到2006-7-1之间举行的所有比赛，并且用以下形式列出：拜仁 2:0 不莱梅 2006-6-21

答：

首先列出需要查询的列：

表team

teamID teamName

表match

match ID

hostTeamID

guestTeamID

matchTime matchResult

其次列出结果列：

主队 结果 客对 时间

初步写一个基础的SQL：

SELECT hostTeamID,matchResult,matchTime guestTeamID from match where matchTime between "2006-6-1" and "2006-7-1";

通过外键联表，完成最终SQL：

select t1.teamName,m.matchResult,t2.teamName,m.matchTime from match as m left join team as t1 on m.hostTeamID = t1.teamID, left join team t2 on m.guestTeamID=t2.guestTeamID where m.matchTime between "2006-6-1" and "2006-7-1"

问题2：UNION与UNION ALL的区别?

答：

如果使用UNION ALL，不会合并重复的记录行

效率 UNION 高于 UNION ALL

问题3：

一个6亿的表a，一个3亿的表b，通过外键tid关联，你如何最快的查询出满足条件的第50000到第50200中的这200条数据记录。

答：

1、如果A表TID是自增长,并且是连续的,B表的ID为索引

select * from a,b where a.tid = b.id and a.tid>50000 limit 200;

2、如果A表的TID不是连续的,那么就需要使用覆盖索引.TID要么是主键,要么是辅助索引,B表ID也需要有索引。

select * from b , (select tid from a limit 50000,200) a where b.id = a .tid;

问题4：拷贝表( 拷贝数据, 源表名：a 目标表名：b)

答：

insert into b(a, b, c) select d,e,f from a;

问题5：

Student(S#,Sname,Sage,Ssex) 学生表

Course(C#,Cname,T#) 课程表

SC(S#,C#,score) 成绩表

Teacher(T#,Tname) 教师表

查询没学过“叶平”老师课的同学的学号、姓名

答：

select Student.S#,Student.Sname

from Student

where S# not in (select distinct( SC.S#) from SC,Course,Teacher where SC.C#=Course.C# and Teacher.T#=Course.T# and Teacher.Tname=’叶平’);

问题6：随机取出10条数据

答：

SELECT * FROM users WHERE id >= ((SELECT MAX(id) FROM users)-(SELECT MIN(id) FROM users)) * RAND() + (SELECT MIN(id) FROM users) LIMIT 10

此方法效率比直接用SELECT * FROM users order by rand() LIMIT 10高很多

需要数据库表1.学生表

Student(SID,Sname,Sage,Ssex) --SID 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别

2.课程表

Course(CID,Cname,TID) --CID --课程编号,Cname 课程名称,TID 教师编号

3.教师表

Teacher(TID,Tname) --TID 教师编号,Tname 教师姓名

4.成绩表

SC(SID,CID,score) --SID 学生编号,CID 课程编号,score 分数

添加测试数据1.学生表

create table Student(SID varchar(10),Sname nvarchar(10),Sage datetime,Ssex nvarchar(10));

insert into Student values('01' , '赵雷' , '1990-01-01' , '男');

insert into Student values('02' , '钱电' , '1990-12-21' , '男');

insert into Student values('03' , '孙风' , '1990-05-20' , '男');

insert into Student values('04' , '李云' , '1990-08-06' , '男');

insert into Student values('05' , '周梅' , '1991-12-01' , '女');

insert into Student values('06' , '吴兰' , '1992-03-01' , '女');

insert into Student values('07' , '郑竹' , '1989-07-01' , '女');

insert into Student values('08' , '王菊' , '1990-01-20' , '女');

2.课程表

create table Course(CID varchar(10),Cname nvarchar(10),TID varchar(10));

insert into Course values('01' , '语文' , '02');

insert into Course values('02' , '数学' , '01');

insert into Course values('03' , '英语' , '03');

3.教师表

create table Teacher(TID varchar(10),Tname nvarchar(10));

insert into Teacher values('01' , '张三');

insert into Teacher values('02' , '李四');

insert into Teacher values('03' , '王五');

4.成绩表

create table SC(SID varchar(10),CID varchar(10),score decimal(18,1));

insert into SC values('01' , '01' , 80);

insert into SC values('01' , '02' , 90);

insert into SC values('01' , '03' , 99);

insert into SC values('02' , '01' , 70);

insert into SC values('02' , '02' , 60);

insert into SC values('02' , '03' , 80);

insert into SC values('03' , '01' , 80);

insert into SC values('03' , '02' , 80);

insert into SC values('03' , '03' , 80);

insert into SC values('04' , '01' , 50);

insert into SC values('04' , '02' , 30);

insert into SC values('04' , '03' , 20);

insert into SC values('05' , '01' , 76);

insert into SC values('05' , '02' , 87);

insert into SC values('06' , '01' , 31);

insert into SC values('06' , '03' , 34);

insert into SC values('07' , '02' , 89);

insert into SC values('07' , '03' , 98);

--1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数--1.1、查询同时存在"01"课程和"02"课程的情况

select a.* , b.score 课程01的分数,c.score 课程02的分数 from Student a , SC b , SC c

where a.SID = b.SID and a.SID = c.SID and b.CID = '01' and c.CID = '02' and b.score > c.score

--1.2、查询同时存在"01"课程和"02"课程的情况和存在"01"课程但可能不存在"02"课程的情况(不存在时显示为null)(以下存在相同内容时不再解释)

select a.* , b.score 课程01的分数,c.score 课程02的分数 from Student a

left join SC b on a.SID = b.SID and b.CID = '01'

left join SC c on a.SID = c.SID and c.CID = '02'

where b.score > isnull(c.score)

--2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数--2.1、查询同时存在"01"课程和"02"课程的情况

select a.* , b.score 课程01的分数 ,c.score 课程02的分数 from Student a , SC b , SC c

where a.SID = b.SID and a.SID = c.SID and b.CID = '01' and c.CID = '02' and b.score < c.score

--2.2、查询同时存在"01"课程和"02"课程的情况和不存在"01"课程但存在"02"课程的情况

select a.* , b.score 课程01的分数 ,c.score 课程02的分数 from Student a

left join SC b on a.SID = b.SID and b.CID = '01'

left join SC c on a.SID = c.SID and c.CID = '02'

where isnull(b.score,0) < c.score

--3、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩

select a.SID , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_score

from Student a , sc b

where a.SID = b.SID

group by a.SID , a.Sname

having cast(avg(b.score) as decimal(18,2)) >= 60

order by a.SID

--4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩--4.1、查询在sc表存在成绩的学生信息的SQL语句。

select a.SID , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_score

from Student a , sc b

where a.SID = b.SID

group by a.SID , a.Sname

having cast(avg(b.score) as decimal(18,2)) < 60

order by a.SID

--4.2、查询在sc表中不存在成绩的学生信息的SQL语句。

select a.SID , a.Sname , isnull(cast(avg(b.score) as decimal(18,2)),0) avg_score

from Student a left join sc b

on a.SID = b.SID

group by a.SID , a.Sname

having isnull(cast(avg(b.score) as decimal(18,2)),0) < 60

order by a.SID

--5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩--5.1、查询所有有成绩的SQL。

select a.SID 学生编号 , a.Sname 学生姓名 , count(b.CID) 选课总数, sum(score) 所有课程的总成绩

from Student a , SC b

where a.SID = b.SID

group by a.SID,a.Sname

order by a.SID

--5.2、查询所有(包括有成绩和无成绩)的SQL。

select a.SID 学生编号 , a.Sname 学生姓名 , count(b.CID) 选课总数, sum(score) 所有课程的总成绩

from Student a left join SC b

on a.SID = b.SID

group by a.SID,a.Sname

order by a.SID

--6、查询"李"姓老师的数量

--方法1

select count(Tname) 李姓老师的数量 from Teacher where Tname like '李%'

--方法2

select count(Tname) 李姓老师的数量 from Teacher where left(Tname,1) = '李'

--7、查询学过"张三"老师授课的同学的信息

select distinct Student.* from Student , SC , Course , Teacher

where Student.SID = SC.SID and SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = '张三'

order by Student.SID

--8、查询没学过"张三"老师授课的同学的信息

select m.* from Student m where SID not in (select distinct SC.SID from SC , Course , Teacher where SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = '张三') order by m.SID

--9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息

--方法1

select Student.* from Student , SC where Student.SID = SC.SID and SC.CID = '01' and exists (Select 1 from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '02') order by Student.SID

--方法2

select Student.* from Student , SC where Student.SID = SC.SID and SC.CID = '02' and exists (Select 1 from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '01') order by Student.SID

--方法3

select m.* from Student m where SID in

(

select SID from

(

select distinct SID from SC where CID = '01'

union all

select distinct SID from SC where CID = '02'

) t group by SID having count(1) = 2

)

order by m.SID

--10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息

--方法1

select Student.* from Student , SC where Student.SID = SC.SID and SC.CID = '01' and not exists (Select 1 from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '02') order by Student.SID

--方法2

select Student.* from Student , SC where Student.SID = SC.SID and SC.CID = '01' and Student.SID not in (Select SC_2.SID from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '02') order by Student.SID

--11、查询没有学全所有课程的同学的信息

--11.1、

select Student.*

from Student , SC

where Student.SID = SC.SID

group by Student.SID , Student.Sname , Student.Sage , Student.Ssex having count(CID) < (select count(CID) from Course)

--11.2

select Student.*

from Student left join SC

on Student.SID = SC.SID

group by Student.SID , Student.Sname , Student.Sage , Student.Ssex having count(CID) < (select count(CID) from Course)

--12、查询至少有一门课与学号为"01"的同学所学相同的同学的信息

select distinct Student.* from Student , SC where Student.SID = SC.SID and SC.CID in (select CID from SC where SID = '01') and Student.SID <> '01'

--13、查询和"01"号的同学学习的课程完全相同的其他同学的信息

select Student.* from Student where SID in

(select distinct SC.SID from SC where SID <> '01' and SC.CID in (select distinct CID from SC where SID = '01')

group by SC.SID having count(1) = (select count(1) from SC where SID='01'))

--14、查询没学过"张三"老师讲授的任一门课程的学生姓名

select student.* from student where student.SID not in

(select distinct sc.SID from sc , course , teacher where sc.CID = course.CID and course.TID = teacher.TID and teacher.tname = '张三')

order by student.SID

--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 student.SID , student.sname , cast(avg(score) as decimal(18,2)) avg_score from student , sc

where student.SID = SC.SID and student.SID in (select SID from SC where score < 60 group by SID having count(1) >= 2)

group by student.SID , student.sname

--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.CID , sc.score from student , sc

where student.SID = SC.SID and sc.score < 60 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--17.1 SQL 2000 静态

select a.SID 学生编号 , a.Sname 学生姓名 ,

max(case c.Cname when '语文' then b.score else null end) 语文 ,

max(case c.Cname when '数学' then b.score else null end) 数学 ,

max(case c.Cname when '英语' then b.score else null end) 英语 ,

cast(avg(b.score) as decimal(18,2)) 平均分

from Student a

left join SC b on a.SID = b.SID

left join Course c on b.CID = c.CID

group by a.SID , a.Sname

order by 平均分 desc

--17.2 SQL 2000 动态

declare @sql nvarchar(4000)

set @sql = 'select a.SID ' + '学生编号' + ' , a.Sname ' + '学生姓名'

select @sql = @sql + ',max(case c.Cname when '''+Cname+''' then b.score else null end) '+Cname+' '

from (select distinct Cname from Course) as t

set @sql = @sql + ' , cast(avg(b.score) as decimal(18,2)) ' + '平均分' + ' from Student a left join SC b on a.SID = b.SID left join Course c on b.CID = c.CID

group by a.SID , a.Sname order by ' + '平均分' + ' desc'

exec(@sql)

--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

--及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90

--方法1

select m.CID 课程编号 , m.Cname 课程名称 ,

max(n.score) 最高分 ,

min(n.score) 最低分 ,

cast(avg(n.score) as decimal(18,2)) 平均分 ,

cast((select count(1) from SC where CID = m.CID and score >= 60)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 及格率 ,

cast((select count(1) from SC where CID = m.CID and score >= 70 and score < 80 )*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 中等率 ,

cast((select count(1) from SC where CID = m.CID and score >= 80 and score < 90 )*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 优良率 ,

cast((select count(1) from SC where CID = m.CID and score >= 90)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 优秀率

from Course m , SC n

where m.CID = n.CID

group by m.CID , m.Cname

order by m.CID

--方法2

select m.CID 课程编号 , m.Cname 课程名称 ,

(select max(score) from SC where CID = m.CID) 最高分 ,

(select min(score) from SC where CID = m.CID) 最低分 ,

(select cast(avg(score) as decimal(18,2)) from SC where CID = m.CID) 平均分 ,

cast((select count(1) from SC where CID = m.CID and score >= 60)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 及格率,

cast((select count(1) from SC where CID = m.CID and score >= 70 and score < 80 )*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 中等率 ,

cast((select count(1) from SC where CID = m.CID and score >= 80 and score < 90 )*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 优良率 ,

cast((select count(1) from SC where CID = m.CID and score >= 90)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 优秀率

from Course m

order by m.CID

--19、按各科成绩进行排序，并显示排名--19.1 sql 2000用子查询完成

--Score重复时保留名次空缺

select t.* , px = (select count(1) from SC where CID = t.CID and score > t.score) + 1 from sc t order by t.cid , px

--Score重复时合并名次

select t.* , px = (select count(distinct score) from SC where CID = t.CID and score >= t.score) from sc t order by t.cid , px

--19.2 sql 2005用rank,DENSE_RANK完成

--Score重复时保留名次空缺(rank完成)

select t.* , px = rank() over(partition by cid order by score desc) from sc t order by t.CID , px

--Score重复时合并名次(DENSE_RANK完成)

select t.* , px = DENSE_RANK() over(partition by cid order by score desc) from sc t order by t.CID , px

--20、查询学生的总成绩并进行排名--20.1 查询学生的总成绩

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(sum(score),0) 总成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

order by 总成绩 desc

--20.2 查询学生的总成绩并进行排名，sql 2000用子查询完成，分总分重复时保留名次空缺和不保留名次空缺两种。

select t1.* , px = (select count(1) from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(sum(score),0) 总成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t2 where 总成绩 > t1.总成绩) + 1 from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(sum(score),0) 总成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t1

order by px

select t1.* , px = (select count(distinct 总成绩) from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(sum(score),0) 总成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t2 where 总成绩 >= t1.总成绩) from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(sum(score),0) 总成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t1

order by px

--20.3 查询学生的总成绩并进行排名，sql 2005用rank,DENSE_RANK完成，分总分重复时保留名次空缺和不保留名次空缺两种。

select t.* , px = rank() over(order by 总成绩 desc) from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(sum(score),0) 总成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t

order by px

select t.* , px = DENSE_RANK() over(order by 总成绩 desc) from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(sum(score),0) 总成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t

order by px

--21、查询不同老师所教不同课程平均分从高到低显示

select m.TID , m.Tname , cast(avg(o.score) as decimal(18,2)) avg_score

from Teacher m , Course n , SC o

where m.TID = n.TID and n.CID = o.CID

group by m.TID , m.Tname

order by 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--22.1 sql 2000用子查询完成

--Score重复时保留名次空缺

select * from (select t.* , px = (select count(1) from SC where CID = t.CID and score > t.score) + 1 from sc t) m where px between 2 and 3 order by m.cid , m.px

--Score重复时合并名次

select * from (select t.* , px = (select count(distinct score) from SC where CID = t.CID and score >= t.score) from sc t) m where px between 2 and 3 order by m.cid , m.px

--22.2 sql 2005用rank,DENSE_RANK完成

--Score重复时保留名次空缺(rank完成)

select * from (select t.* , px = rank() over(partition by cid order by score desc) from sc t) m where px between 2 and 3 order by m.CID , m.px

--Score重复时合并名次(DENSE_RANK完成)

select * from (select t.* , px = DENSE_RANK() over(partition by cid order by score desc) from sc t) m where px between 2 and 3 order by m.CID , m.px

--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 --23.1 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

--横向显示

select Course.CID 课程编号 , Cname as 课程名称 ,

sum(case when score >= 85 then 1 else 0 end) 85-100 ,

sum(case when score >= 70 and score < 85 then 1 else 0 end) 70-85 ,

sum(case when score >= 60 and score < 70 then 1 else 0 end) 60-70 ,

sum(case when score < 60 then 1 else 0 end) 0-60

from sc , Course

where SC.CID = Course.CID

group by Course.CID , Course.Cname

order by Course.CID

--纵向显示1(显示存在的分数段)

select m.CID 课程编号 , m.Cname 课程名称 , 分数段 = (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end) ,

count(1) 数量

from Course m , sc n

where m.CID = n.CID

group by m.CID , m.Cname , (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end)

order by m.CID , m.Cname , 分数段

--纵向显示2(显示存在的分数段，不存在的分数段用0显示)

select m.CID 课程编号 , m.Cname 课程名称 , 分数段 = (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end) ,

count(1) 数量

from Course m , sc n

where m.CID = n.CID

group by all m.CID , m.Cname , (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end)

order by m.CID , m.Cname , 分数段

--23.2 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 , <60 及所占百分比

--横向显示

select m.CID 课程编号, m.Cname 课程名称,

(select count(1) from SC where CID = m.CID and score < 60) 0-60 ,

cast((select count(1) from SC where CID = m.CID and score < 60)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 百分比 ,

(select count(1) from SC where CID = m.CID and score >= 60 and score < 70) 60-70 ,

cast((select count(1) from SC where CID = m.CID and score >= 60 and score < 70)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 百分比 ,

(select count(1) from SC where CID = m.CID and score >= 70 and score < 85) 70-85 ,

cast((select count(1) from SC where CID = m.CID and score >= 70 and score < 85)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 百分比 ,

(select count(1) from SC where CID = m.CID and score >= 85) 85-100 ,

cast((select count(1) from SC where CID = m.CID and score >= 85)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 百分比

from Course m

order by m.CID

--纵向显示1(显示存在的分数段)

select m.CID 课程编号 , m.Cname 课程名称 , 分数段 = (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end) ,

count(1) 数量 ,

cast(count(1) * 100.0 / (select count(1) from sc where CID = m.CID) as decimal(18,2)) 百分比

from Course m , sc n

where m.CID = n.CID

group by m.CID , m.Cname , (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end)

order by m.CID , m.Cname , 分数段

--纵向显示2(显示存在的分数段，不存在的分数段用0显示)

select m.CID 课程编号 , m.Cname 课程名称 , 分数段 = (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end) ,

count(1) 数量 ,

cast(count(1) * 100.0 / (select count(1) from sc where CID = m.CID) as decimal(18,2)) 百分比

from Course m , sc n

where m.CID = n.CID

group by all m.CID , m.Cname , (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end)

order by m.CID , m.Cname , 分数段

--24、查询学生平均成绩及其名次--24.1 查询学生的平均成绩并进行排名，sql 2000用子查询完成，分平均成绩重复时保留名次空缺和不保留名次空缺两种。

select t1.* , px = (select count(1) from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t2 where 平均成绩 > t1.平均成绩) + 1 from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t1

order by px

select t1.* , px = (select count(distinct 平均成绩) from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t2 where 平均成绩 >= t1.平均成绩) from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t1

order by px

--24.2 查询学生的平均成绩并进行排名，sql 2005用rank,DENSE_RANK完成，分平均成绩重复时保留名次空缺和不保留名次空缺两种。

select t.* , px = rank() over(order by 平均成绩 desc) from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t

order by px

select t.* , px = DENSE_RANK() over(order by 平均成绩 desc) from

(

select m.SID 学生编号 ,

m.Sname 学生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成绩

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t

order by px

--25、查询各科成绩前三名的记录--25.1 分数重复时保留名次空缺

select m.* , n.CID , n.score from Student m, SC n where m.SID = n.SID and n.score in

(select top 3 score from sc where CID = n.CID order by score desc) order by n.CID , n.score desc

--25.2 分数重复时不保留名次空缺，合并名次

--sql 2000用子查询实现

select * from (select t.* , px = (select count(distinct score) from SC where CID = t.CID and score >= t.score) from sc t) m where px between 1 and 3 order by m.Cid , m.px

--sql 2005用DENSE_RANK实现

select * from (select t.* , px = DENSE_RANK() over(partition by Cid order by score desc) from sc t) m where px between 1 and 3 order by m.CID , m.px

--26、查询每门课程被选修的学生数

select Cid , count(SID) 学生数 from sc group by CID

--27、查询出只有两门课程的全部学生的学号和姓名

select Student.SID , Student.Sname

from Student , SC

where Student.SID = SC.SID

group by Student.SID , Student.Sname

having count(SC.CID) = 2

order by Student.SID

--28、查询男生、女生人数

select count(Ssex) as 男生人数 from Student where Ssex = N'男'

select count(Ssex) as 女生人数 from Student where Ssex = N'女'

select sum(case when Ssex = N'男' then 1 else 0 end) 男生人数 ,sum(case when Ssex = N'女' then 1 else 0 end) 女生人数 from student

select case when Ssex = N'男' then N'男生人数' else N'女生人数' end 男女情况 , count(1) 人数 from student group by case when Ssex = N'男' then N'男生人数' else N'女生人数' end

--29、查询名字中含有"风"字的学生信息

select * from student where sname like N'%风%'

select * from student where charindex(N'风' , sname) > 0

--30、查询同名同性学生名单，并统计同名人数

select Sname 学生姓名 , count(*) 人数 from Student group by Sname having count(*) > 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 * from Student where year(sage) = 1990

select * from Student where datediff(yy,sage,'1990-01-01') = 0

select * from Student where datepart(yy,sage) = 1990

select * from Student where convert(varchar(4),sage,120) = '1990'

--32、查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列

select m.CID , m.Cname , cast(avg(n.score) as decimal(18,2)) avg_score

from Course m, SC n

where m.CID = n.CID

group by m.CID , m.Cname

order by avg_score desc, m.CID asc

--33、查询平均成绩大于等于85的所有学生的学号、姓名和平均成绩

select a.SID , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_score

from Student a , sc b

where a.SID = b.SID

group by a.SID , a.Sname

having cast(avg(b.score) as decimal(18,2)) >= 85

order by a.SID

--34、查询课程名称为"数学"，且分数低于60的学生姓名和分数

select sname , score

from Student , SC , Course

where SC.SID = Student.SID and SC.CID = Course.CID and Course.Cname = N'数学' and score < 60

--35、查询所有学生的课程及分数情况

select Student.* , Course.Cname , SC.CID , SC.score

from Student, SC , Course

where Student.SID = SC.SID and SC.CID = Course.CID

order by Student.SID , SC.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 Student.* , Course.Cname , SC.CID , SC.score

from Student, SC , Course

where Student.SID = SC.SID and SC.CID = Course.CID and SC.score >= 70

order by Student.SID , SC.CID

--37、查询不及格的课程

select Student.* , Course.Cname , SC.CID , SC.score

from Student, SC , Course

where Student.SID = SC.SID and SC.CID = Course.CID and SC.score < 60

order by Student.SID , SC.CID

--38、查询课程编号为01且课程成绩在80分以上的学生的学号和姓名

select Student.* , Course.Cname , SC.CID , SC.score

from Student, SC , Course

where Student.SID = SC.SID and SC.CID = Course.CID and SC.CID = '01' and SC.score >= 80

order by Student.SID , SC.CID

--39、求每门课程的学生人数

select Course.CID , Course.Cname , count(*) 学生人数

from Course , SC

where Course.CID = SC.CID

group by Course.CID , Course.Cname

order by Course.CID , Course.Cname

--40、查询选修"张三"老师所授课程的学生中，成绩最高的学生信息及其成绩--40.1 当最高分只有一个时

select top 1 Student.* , Course.Cname , SC.CID , SC.score

from Student, SC , Course , Teacher

where Student.SID = SC.SID and SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = N'张三'

order by SC.score desc

--40.2 当最高分出现多个时

select Student.* , Course.Cname , SC.CID , SC.score

from Student, SC , Course , Teacher

where Student.SID = SC.SID and SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = N'张三' and

SC.score = (select max(SC.score) from SC , Course , Teacher where SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = N'张三')

--41、查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩

--方法1

select m.* from SC m ,(select CID , score from SC group by CID , score having count(1) > 1) n

where m.CID= n.CID and m.score = n.score order by m.CID , m.score , m.SID

--方法2

select m.* from SC m where exists (select 1 from (select CID , score from SC group by CID , score having count(1) > 1) n

where m.CID= n.CID and m.score = n.score) order by m.CID , m.score , m.SID

--42、查询每门功成绩最好的前两名

select t.* from sc t where score in (select top 2 score from sc where CID = T.CID order by score desc) order by t.CID , t.score desc

--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 Course.CID , Course.Cname , count(*) 学生人数

from Course , SC

where Course.CID = SC.CID

group by Course.CID , Course.Cname

having count(*) >= 5

order by 学生人数 desc , Course.CID

--44、检索至少选修两门课程的学生学号

select student.SID , student.Sname

from student , SC

where student.SID = SC.SID

group by student.SID , student.Sname

having count(1) >= 2

order by student.SID

--45、查询选修了全部课程的学生信息

--方法1 根据数量来完成

select student.* from student where SID in

(select SID from sc group by SID having count(1) = (select count(1) from course))

--方法2 使用双重否定来完成

select t.* from student t where t.SID not in

(

select distinct m.SID from

(

select SID , CID from student , course

) m where not exists (select 1 from sc n where n.SID = m.SID and n.CID = m.CID)

)

--方法3 使用双重否定来完成

select t.* from student t where not exists(select 1 from

(

select distinct m.SID from

(

select SID , CID from student , course

) m where not exists (select 1 from sc n where n.SID = m.SID and n.CID = m.CID)

) k where k.SID = t.SID

)

--46、查询各学生的年龄--46.1 只按照年份来算

select * , datediff(yy , sage , getdate()) 年龄 from student

--46.2 按照出生日期来算，当前月日

select * , case when right(convert(varchar(10),getdate(),120),5) < right(convert(varchar(10),sage,120),5) then datediff(yy , sage , getdate()) - 1 else datediff(yy , sage , getdate()) end 年龄 from student

--47、查询本周过生日的学生

select * from student where datediff(week,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = 0

--48、查询下周过生日的学生

select * from student where datediff(week,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = -1

--49、查询本月过生日的学生

select * from student where datediff(mm,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = 0

--50、查询下月过生日的学生

select * from student where datediff(mm,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = -1