41道题：
重要的
连表查询
分组
制表语句：
班级表
Table: class
Create Table: CREATE TABLE `class` (
`cid` int(11) NOT NULL AUTO_INCREMENT,
`caption` varchar(50) DEFAULT NULL,
PRIMARY KEY (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
学生表：
Table: student
Create Table: CREATE TABLE `student` (
`sid` int(11) NOT NULL AUTO_INCREMENT,
`sname` varchar(50) DEFAULT NULL,
`gender` char(10) DEFAULT NULL,
`class_id` int(11) DEFAULT NULL,
PRIMARY KEY (`sid`),
KEY `fk_student_class` (`class_id`),
CONSTRAINT `fk_student_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
老师表：
Table: teacher
Create Table: CREATE TABLE `teacher` (
`tid` int(11) NOT NULL AUTO_INCREMENT,
`tname` varchar(50) DEFAULT NULL,
PRIMARY KEY (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
课程表：
Table: course
Create Table: CREATE TABLE `course` (
`cid` int(11) NOT NULL AUTO_INCREMENT,
`cname` char(25) DEFAULT NULL,
`teacher_id` int(11) DEFAULT NULL,
PRIMARY KEY (`cid`),
KEY `fk_course_teacher` (`teacher_id`),
CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
成绩表：
create table score
(sid int not null auto_increment primary key,
student_id int not null,
corse_id int not null,
number int not null,
unique uq_sc (student_id,corse_id),
CONSTRAINT fk_sc_st FOREIGN key (student_id) REFERENCES student(sid),
constraint fk_sc_co foreign key (corse_id) references course(cid)
) engine=innodb default charset=utf8;
group by前面的slect 只能用聚合函数count,max什么的
v= 111 if 1==1 else 110 三元运算符
#########################################################
作业练习：
http://www.cnblogs.com/wupeiqi/articles/5729934.html
http://www.cnblogs.com/wupeiqi/p/5748496.html 参考答案
##########################################################
用到的知识点
- 临时表
select * from (select * from tb where id< 10) as B;
---
select
id,
name,
1,
(select count(1) from tb)----只要拿到的是一个值就可以
from tb2
---把最外层的表s1，每次循环取一个常量值再到每一列中再循环一次
SELECT
student_id,
(select num from score as s2 where s2.student_id=s1.student_id and course_id = 1) as 语文,
(select num from score as s2 where s2.student_id=s1.student_id and course_id = 2) as 数学,
(select num from score as s2 where s2.student_id=s1.student_id and course_id = 3) as 英语
from score as s1;
----avg(if(isnull(score.num),0,score.num))
三目运算符
#####################################################
具体作业：
1、自行创建测试数据
2、查询“生物”课程比“物理”课程成绩高的所有学生的学号；
PS：查出生物课程的学生，查出物理课程的学生，用临时表，再连接查询
select A.student_id from
(select * from score
LEFT JOIN course on score.course_id=course.cid
where course.cname="生物"
) as A
LEFT JOIN
(select * from score
LEFT JOIN course on score.course_id=course.cid
where course.cname="物理"
) as B
on A.student_id=B.student_id
where A.num> B.num
3、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(num) from score GROUP BY student_id
PS:把名字也带上
select S.student_id,student.sname,S.av_s from
(SELECT student_id, avg(num) AS av_s FROM score GROUP BY student_id HAVING av_s > 60) as S
LEFT JOIN student on student.sid=S.student_id
4、查询所有同学的学号、姓名、选课数、总成绩；
SELECT score.student_id,student.sname, COUNT(score.student_id),sum(score.num) from score
LEFT JOIN student ON score.student_id=student.sid
GROUP BY score.student_id
5、查询姓“李”的老师的个数；
select COUNT(*) from teacher where teacher.tname
LIKE "李%"
6、查询没学过“李平老师“课的同学的学号、姓名；
PS：先查找李平的课程ID，再到score表中找学他的课的学生Id，再去student表中全部排除
select student.sid,student.sname from student
where student.sid not in
(
select score.student_id from score
where course_id in (select course.cid from course
LEFT JOIN teacher on teacher.tid=course.cid
where teacher.tname="李平老师")
)
7、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；
PS：找出score表中学过课程1，或者2，或者1,2的学生，分组找出大于2的，再与学生表进行连接查询
select student.sid,student.sname from score
LEFT JOIN student on score.student_id=student.sid
where score.course_id=1 or score.course_id=2 GROUP BY score.student_id HAVING count(score.course_id)>1
8、查询学过“叶平”老师所教的所有课的同学的学号、姓名；
PS：语句分两部分B表是查出学过叶平老师所有课程的学生ID（注意其中叶平的课程有所变化所以不能count >2）
再与学生表进行关联
SELECT student.sid,student.sname FROM student
LEFT JOIN
(
SELECT score.student_id FROM score WHERE score.course_id
IN (
SELECT cid FROM course
LEFT JOIN teacher ON teacher.tid = course.teacher_id
WHERE teacher.tname = "李平老师"
) --查出叶平老师所教的课程的ID
GROUP BY score.student_id
HAVING
count(score.student_id) =
(
SELECT count(cid) FROM course LEFT JOIN teacher ON teacher.tid = course.teacher_id
WHERE teacher.tname = "李平老师"
) --查出叶平老师总共教了几门课count(cid)
) AS B --查出学过叶平老师所有课程的学生ID
ON student.sid = B.student_id
9、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；
PS:
select student.sid,student.sname from student
left JOIN
(select A.student_id from
(select * from score
LEFT JOIN course on score.course_id=course.cid
where course.cid=1
) as A
LEFT JOIN
(select * from score
LEFT JOIN course on score.course_id=course.cid
where course.cid=2
) as B
on A.student_id=B.student_id
where A.num<B.num
) as C
on student.sid=C.student_id
10、查询有课程成绩小于60分的同学的学号、姓名；
select sid,sname from student where sid in (
select distinct student_id from score where num < 60
)
11、查询没有学全所有课的同学的学号、姓名；
PS ---count要嘛用1要嘛用主键，效率高
SELECT student.sid,student.sname from student
INNER JOIN
(
select score.student_id,count(1) from score GROUP BY score.student_id HAVING count(1) < (SELECT count(cid) from course)
) as B
on student.sid = B.student_id
12、查询至少有一门课与学号为“001”的同学所学相同的同学的学号和姓名；
select student.sid,student.sname from student
INNER JOIN
(
SELECT score.student_id,score.course_id from score where score.student_id !=1
and score.course_id in (select score.course_id from score where score.student_id=1) GROUP BY score.student_id
) as B
on student.sid=B.student_id
13、查询至少学过学号为“001”同学所有课的其他同学学号和姓名
select student.sid,student.sname from student
INNER JOIN
(
SELECT score.student_id,count(1) from score where score.student_id !=1
and score.course_id in (select score.course_id from score where score.student_id=1)
GROUP BY score.student_id
HAVING count(1) = (select count(1) from score where score.student_id=1)
) AS B
on student.sid=B.student_id
14、查询和“002”号的同学学习的课程完全相同的其他同学学号和姓名；
SELECT student_id from score where student_id
in (
select student_id from score where student_id !=2 GROUP BY student_id
HAVING COUNT(1) =(select count(1) from score where student_id=1)
)
and course_id in (SELECT course_id from score where student_id =2)
GROUP BY student_id HAVING COUNT(1) = (SELECT count(1) from score where student_id)
15、删除学习“叶平”老师课的SC表记录；
delete from score where course_id in
(
select cid from course left join teacher on course.teacher_id = teacher.tid where teacher.name = ‘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：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,course_id,num)
VALUES(select student_id,2,(select AVG(num) from score where course_id = 2) from score where course_id !=2)
17、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 s1.student_id,
(select num from score left join course on score.course_id = course.cid where course.cname = "生物" and score.student_id=s1.student_id) as 生物,
(select num from score left join course on score.course_id = course.cid where course.cname = "物理" and score.student_id=s1.student_id) as 物理,
(select num from score left join course on score.course_id = course.cid where course.cname = "体育" and score.student_id=s1.student_id) as 体育,
count(s1.course_id),
avg(s1.num)
from score as s1
group by student_id 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 course_id,MAX(num),min(num) from score GROUP BY course_id
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
course_id,avg(num),
sum(case when num <60 THEN 0 ELSE 1 END),sum(1),
sum(case when num <60 THEN 0 ELSE 1 END)/sum(1) as jgl
from score GROUP BY course_id order by AVG(num) asc,jgl desc;
20、课程平均分从高到低显示（现实任课老师）；
select
course_id,avg(num),teacher.tname
from score
LEFT JOIN course on score.course_id=course.cid
left JOIN teacher on teacher.tid = course.teacher_id
GROUP BY course_id desc
select avg(if(isnull(score.num),0,score.num)),teacher.tname from course
left join score on course.cid = score.course_id
left join teacher on course.teacher_id = teacher.tid
group by score.course_id
21、查询各科成绩前三名的记录:(不考虑成绩并列情况)
22、查询每门课程被选修的学生数；
SELECT student_id ,count(1) from score GROUP BY course_id HAVING COUNT(1) >5
23、查询出只选修了一门课程的全部学生的学号和姓名；
SELECT student.sid,student.sname from student
INNER JOIN
(SELECT student_id ,count(1) from score GROUP BY student_id HAVING COUNT(1) =1) as B
on student.sid=B.student_id
24、查询男生、女生的人数；
SELECT gender,COUNT(1) from student GROUP BY gender
25、查询姓“张”的学生名单；
SELECT sname from student where sname LIKE "张%"
26、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
27、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 course_id,AVG(num) from score GROUP BY score.course_id ORDER BY avg(num) ASC,course_id DESC
28、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 sid,sname,T.B from student
INNER JOIN
(SELECT student_id ,avg(if(ISNULL(num) ,0,num)) as B from score GROUP BY student_id HAVING B >85) as T
on T.student_id=student.sid
29、查询课程名称为“生物”，且分数低于60的学生姓名和分数；
SELECT student.sname,score.num from course
LEFT JOIN score on course.cid=score.course_id
LEFT JOIN student on student.sid=score.student_id
where course.cname=‘生物‘ and score.num < 60
30、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 student.sname,score.num from course
LEFT JOIN score on course.cid=score.course_id
LEFT JOIN student on student.sid=score.student_id
where course.cid=3 and score.num >80
31、求选了课程的学生人数
SELECT count(DISTINCT(score.student_id)) from score
32、查询选修“李平”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,T.num from student
INNER JOIN
(SELECT * from teacher
LEFT JOIN course on teacher.tid=course.teacher_id
LEFT JOIN score on score.course_id=course.cid
GROUP BY num HAVING teacher.tname="张磊老师" ORDER BY num DESC LIMIT 0,1) as T
on student.sid= T.student_id
33、查询各个课程及相应的选修人数；
select course.cname,count(1) from score
left join course on score.course_id = course.cid
group by course_id;
34、查询不同课程但成绩相同的学生的学号、课程号、学生成绩；
SELECT DISTINCT s1.student_id,s1.course_id,s1.num from score as s1,score as s2 WHERE s1.sid !=s2.sid and s1.course_id !=s2.course_id and s1.num=s2.num
35、查询每门课程成绩最好的前两名；
select score.sid,score.course_id,score.num,T.first_num,T.second_num from score left join
(
select
sid,
(select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 0,1) as first_num,
(select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 1,1) as second_num
from
score as s1
) as T
on score.sid =T.sid
where score.num <= T.first_num and score.num >= T.second_num
36、检索至少选修两门课程的学生学号；
SELECT student_id from score GROUP BY student_id HAVING count(student_id) >1
37、查询全部学生都选修的课程的课程号和课程名；
38、查询没学过“叶平”老师讲授的任一门课程的学生姓名；
PS：先查出学过李平老师任意一门课的学生，包括只选了一门的，然后，全部排除
SELECT student.sid from student
WHERE sid not in(
SELECT score.student_id from score
WHERE course_id in
(
SELECT course.cid from course
LEFT JOIN teacher on course.teacher_id=teacher.tid WHERE teacher.tname="李平老师"
))
39、查询两门以上不及格课程的同学的学号及其平均成绩；
select student_id,count(1) from score where num < 60 group by student_id having count(1) > 2
40、检索“004”课程分数小于60，按分数降序排列的同学学号；
select student_id from score where num< 60 and course_id = 4 order by num desc;
41、删除“002”同学的“001”课程的成绩；
delete from score where course_id = 1 and student_id = 2
时间： 2024-10-19 05:52:39