标签：group by   老师   ref   sum   delete   sele   count   style   when   

建立5个表    

CREATE TABLE class (
cid INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
caption VARCHAR(20)
)
INSERT INTO class (caption) VALUE (‘三年二班‘);
INSERT INTO class (caption) VALUE (‘一年三班‘);
INSERT INTO class (caption) VALUE (‘三年一班‘);

CREATE TABLE student (
sid INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
sname VARCHAR(20),
gender VARBINARY(3),
class_id INT,
CONSTRAINT fk_idclass_id FOREIGN KEY (class_id) REFERENCES class(cid)
)
INSERT INTO student (sname, gender ,class_id) VALUE (‘钢蛋‘,‘女‘,‘1‘);
INSERT INTO student (sname, gender ,class_id) VALUE (‘铁锤‘,‘女‘,‘1‘);
INSERT INTO student (sname, gender ,class_id) VALUE (‘山炮‘,‘男‘,‘2‘);

CREATE TABLE teacher (
tid INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
tname VARCHAR(20)
)
INSERT INTO teacher (tname) VALUE (‘波动‘);
INSERT INTO teacher (tname) VALUE (‘皆空‘);
INSERT INTO teacher (tname) VALUE (‘虚无‘);

CREATE TABLE scourse (
cid INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
cname VARCHAR(20)，
tearch_id INT,
CONSTRAINT fk_idteacher_tid FOREIGN KEY (teacher_id) REFERENCES teacher(tid)
)
INSERT INTO scourse (cname, teacher_id) VALUE (‘生物‘,‘1‘);
INSERT INTO scourse (cname, teacher_id) VALUE (‘体育‘,‘1‘);
INSERT INTO scourse (cname, teacher_id) VALUE (‘物理‘,‘2‘);

CREATE TABLE score(
sid INT AUTO_INCREMENT PRIMARY KEY,
student_id INT ,
corse_id INT ,
number INT,
UNIQUE uq_st_cor (student_id,corse_id),
CONSTRAINT fk_student_sid FOREIGN KEY (student_id) REFERENCES student(sid),
CONSTRAINT fk_corse_cid FOREIGN KEY (corse_id) REFERENCES scourse(cid)

)
INSERT INTO score (student_id, corse_id, number) VALUE (1, 1, 60),(1, 2, 59), (2, 2, 100);

总结：题型

-比较（一个表中只能左右比较 不能上下比较，所以要连表） 1

-创建一条崭新的数据列(即列表无的数据)   7，21, 25 

 -查找数据2 ，4，16， 17，18，19，30

-case when 类型（发现sise， 哈哈） 22 ，23  -

-通配符 27

#1t生物成绩比体育成绩高的学生学号

select A.student_id from 

(select  score.sid ,score.student_id,cname,number  from  scourse    

left join score on score.corse_id = scourse.cid   

where cname = "生物"）as A

 left join 

(select  score.sid ,score.student_id,cname,number  from  scourse    

left join score on score.corse_id = scourse.cid   

where cname = "体育") as B

 on   A.student_id = B.student_id

where  A.number < B.number

#2查询平均成绩大于60分的同学的学号和平均成绩

SELECT student_id ,AVG(number) FROM score GROUP BY student_id HAVING AVG(number)>60  

加上学生姓名

select  cname ,student_id from

（SELECT student_id ,AVG(number) FROM score GROUP BY student_id HAVING AVG(number)>60  ）as A

left join  student on student.sid = A.studend_id

#3.所有同学的学号 姓名 课程数目

select  student_id ,sname ,count(1 )  from score  left join student on student.sid = score.student_id  group by student_id

#4查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；

select  student_id ,sname  from 

(select student_id  from  score where corse_id =1 or corse_id  =2  group  by corse_id   having count (1) >1) as A

left join  student   on student.sid  = A.student_id 

#5查询有课程成绩小于60分的同学的学号、姓名；

select  student_id ,sname  from 

(select  student_id  from  score where number <60)  as A

left join  student   on student.sid  = A.student_id 

#6删除“001”同学的“001”课程的成绩；

DELETE FROM score  WHERE  corse_id=1 AND student_id=1;

#7查询一门课程成绩最好的前两名；

select  student_id ,  corse_id,

(select number from score as b  where b.corse_id =a.corse_id   group by b.number  order by  b.number  desc  limit 0,1 ) as first,

(select number from score as b where b.corse_id = a.corse_id group by b.number order by b.number desc limit 1,1 ) as second

from score as a;

#8查询男生、女生的人数；

select gendert ,count(1) from student group by gender 

#9查询出只选修了一门课程的全部学生的学号和姓名；

select  student_id,sname from 

(select * from score group by corse_id  having count(1) =1) as A

left join student on student.sid = A.student_id

#10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 student_id,MAX(number),MIN(number) ,AVG(number) FROM score
LEFT JOIN student ON score.student_id=student.sid
LEFT JOIN scourse ON score.corse_id = scourse.cid
LEFT JOIN class ON student.class_id = class.cid
LEFT JOIN teacher ON scourse.teacher_id = teacher.tid
GROUP BY corse_id

#11课程平均分从高到低显示（现实任课老师）；

select  corse_id,avg(number) from  score   group by corse_id    order by avg(number )  desc        

#12所有同学的学号 姓名 课程数目

SELECT student_id , student.sname , COUNT(1) FROM score 

LEFT JOIN student ON student.sid = score.student_id GROUP BY student_id

#13查询那个同学没上过某某老师的课

select  * from score where corse_id not in 

(select cid from scourse  left  join teacher on scourse.teacher_id = teacher.tid  where teacher.tname = "波动")

#14查询选过某某老师全部课程的同学学号

SELECT student_id FROM score WHERE corse_id IN
(SELECT cid FROM scourse LEFT JOIN teacher ON teacher.tid = scourse.teacher_id WHERE teacher.tname = ‘波动‘)
GROUP BY student_id HAVING COUNT(1) = (SELECT COUNT(1) FROM scourse LEFT JOIN teacher ON teacher.tid = scourse.teacher_id WHERE teacher.tname = ‘波动‘)

#15查询不及格的同学

SELECT student_id FROM score WHERE number < ‘60‘ GROUP 

#16 查询没有学全的同学

SELECT student_id,COUNT(1) FROM score
GROUP BY (student_id) HAVING COUNT(1) <
(SELECT COUNT(1) FROM scourse )

#17 查询至少学过一门课和学号为1的同学所学的课程相同的同学

SELECT student_id FROM score WHERE student_id !=1

AND corse_id IN (SELECT corse_id FROM score WHERE student_id =1 ) GROUP BY student_id

#18 查询至少学过一门课和学号为1的同学所学的课程所有课程的同学

SELECT student_id,count(1) FROM score WHERE student_id !=1

AND corse_id IN (SELECT corse_id FROM score WHERE student_id =1 ) GROUP BY student_id
HAVING COUNT(1)=(SELECT count(corse_id) FROM score WHERE student_id =1 )

#19查询和“001”号的同学学习的课程完全相同的其他同学学号和姓名

第一步  找出课程个数相同的同学

select studednt_id from score where student_id != 1 group by student_id having 

count(1) = (select count(1) from score where student_id = 1)

第二步  个数相同且课程相同的同学

select * from score where student_id  in (

select studednt_id from score where student_id != 1 group by student_id having 

count(1) = (select count(1) from score where student_id = 1)

) and corse_id  in ( select corse_id from score where student_id =1 )

#20

向SC表中插入一些记录，这些记录要求符合以下条件：①没有上过编号“002”课程的同学学号；②插入“002”号课程的平均成绩； 

insert into score(student_id,corse_id,number)  
select student_id, 2 , (SELECT AVG(number) FROM score WHERE corse_id =2 ) from score where corse_id !=2

#21、

按平均成绩从低到高显示所有学生的“语文”、“数学”、“英语”三门的课程成绩，按如下形式显示： 学生ID,语文,数学,英语,有效课程数,有效平均分；

select
student_id,
(select number from score as b where b.student_id = a.student_id and corse_id = 1 ) as 语文,
(SELECT number FROM score AS b WHERE b.student_id = a.student_id AND corse_id = 2 ) as 数学,
(SELECT number FROM score AS b WHERE b.student_id = a.student_id AND corse_id = 3 )as 英语

from score as a group by student_id

#22、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 corse_id , max(number) , min(number ),
case when min(number)=59 then 60 else min(number) end as  sise秘密
from score group by student_id

#23、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  corse_id ,avg(number),

sum(case when number >= 60 then 1 else 0 end )/sum(1) as 及格率

from socre group by corse_id order by avg(number ) asc  ，  及格率 desc;

#24、课程平均分从高到低显示（现实任课老师）；

select corse_id ,avg(number) , teacher.tname from score
left join scourse on scourse.cid = score.corse_id
left join teacher on teacher.tid = scourse.teacher_id
group by corse_id

#25、查询各科成绩前两 名的记录:(不考虑成绩并列情况) 

（
select
student_id,
corse_id,
(select number from score as b where b.corse_id=a.corse_id group by b.number order by b.number desc limit 0,1 ) as first ,
(SELECT number FROM score AS b WHERE b.corse_id=a.corse_id GROUP BY b.number ORDER BY b.number DESC LIMIT 1,1 )as second

from score as a;
）

#26、查询出只选修了一门课程的全部学生的学号和姓名；

select student_id, count(1) from score  group by student_id having count(1) =1

#27、查询姓“张”的学生名单；

select sname from student where sname   like "钢%" 

#28、查询同名同姓学生名单，并统计同名人数；

select sname,count(1) from student group by sname 

#29、查询全部学生都选修的课程的课程号和课程名；

select * from score as a, score as b where
a.sid != b.sid and a.corse_id = b.corse_id group by corse_id

select corse_id from score group by corse_id
having count(corse_id)=
(select count(sname) from student )

#30、查询没学过“叶平”老师讲授的任一门课程的学生姓名；

select * from student where sid not in
(select student_id from score
left join student on student.sid = score.student_id
WHERE corse_id IN
(SELECT cid FROM scourse
LEFT JOIN teacher ON teacher.`tid`= scourse.`teacher_id`
WHERE tname= "波动")
)

总结：题型

-比较（一个表中只能左右比较 不能上下比较，所以要连表） 1

-创建一条崭新的数据列(即列表无的数据)   7，21, 25 

 -查找数据2 ，4，16， 17，18，19，30

-case when 类型（发现sise， 哈哈） 22 ，23  -

-通配符 27

Mysql学习日记-03sql语句练习

标签：group by   老师   ref   sum   delete   sele   count   style   when   

原文地址：https://www.cnblogs.com/kangkang1999/p/13232898.html