数据表介绍
--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
学生表 Student
create table Student(SId varchar(10),Sname varchar(10),Sage datetime,Ssex varchar(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','1990-12-20','男');
insert into Student values('04','李云','1990-12-06','男');
insert into Student values('05','周梅','1991-12-01','女');
insert into Student values('06','吴兰','1992-01-01','女');
insert into Student values('07','郑竹','1989-01-01','女');
insert into Student values('08','张三','2017-12-20','女');
insert into Student values('09','张三','1991-10-10','男')
科目表 Course
create table Course(CId varchar(10),Cname varchar(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');
教师表 Teacher
create table Teacher(TId varchar(10),Tname varchar(10));
insert into Teacher values('01','张三');
insert into Teacher values('02','李四');
insert into Teacher values('03','王五');
成绩表 SC
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);
练习题目
- 查询" 01 "课程比" 02 "课程成绩高的所有学生的学号
找出课程01和课程02的信息，筛选条件01的成绩比02高，并且Sid相同
select a.sid from (select sid,score from SC where cid=01) a,
(select sid,score from SC where cid=02) b
where a.score>b.score and a.sid=b.sid
1.1 查询同时存在" 01 "课程和" 02 "课程的情况
找出课程01和课程02的信息，筛选条件Sid相同
select * from (select * from SC where cid=01) as a,
(select * from SC where cid=02) as b
where a.sid=b.sid
1.2 查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为 null )
找出01的课程记录，然后与其他表关联，考察left join
select * from
(select * from SC where cid=01) a
left join sc b
on a.Sid= b.Sid and b.cid=02;
1.3 查询不存在" 01 "课程但存在" 02 "课程的情况
思路1.找出01的课程记录，取反值筛选出不是01课程，关联其他表，考察inner join
select * from
(select *from sc where sid not in (select sid from SC where cid=01)) a
inner join sc b
on a.Sid = b.Sid and b.cid=02;;
思路2.找出不学01课程的信息，再找出其中包含02课程的情况
select * from sc
where sid not in (select sid from sc where cid=01) and cid=02;
- 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 sc.sid,sname,avg(score)
from sc join student as a
on sc.sid= a.sid
group by sc.sid
having avg(score)>=60;
- 查询在 SC 表存在成绩的学生信息
select * from student
where sid in
(select sid from sc group by sid)
- 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(没成绩的显示为 null )
select a.sid ,sname,sum_score,count_c from
student b left join
(select sid,sum(score) as sum_score,count(cid) as count_c
from sc
group by sid) a
on a.sid =b.sid
4.1 查有成绩的学生信息
select a.sid ,sname,sum_score,count_c from
student b inner join
(select sid,sum(score) as sum_score,count(cid) as count_c
from sc
group by sid) a
on a.sid =b.sid
- 查询「李」姓老师的数量
select count(1)
from teacher
where Tname like"李%"
- 查询学过「张三」老师授课的同学的信息
思路1.嵌套子查询
select * from student
where sid in
(select sid from sc
where cid in
(select cid from course
where tid in
(select tid from teacher
where tname='张三')))
思路2.将四张表关联，再设筛选条件
select * from student a
inner join sc b
inner join course c
inner join teacher d
on a.sid=b.sid and b.cid=c.cid and c.tid= d.tid
where tname='张三'
- 查询没有学全所有课程的同学的信息
查出学全所有课程的同学的信息，再排除
select * from student c
where c.sid not in (select a.sid from student a
inner join sc b
on a.sid= b.sid
group by b.sid
having count(b.cid)>2);
- 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 a.* from student a
inner join sc b
on a.sid=b.sid
where cid in (select cid from sc
where sid=01) and b.sid!=01;
- 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
思路：排除学习了01同学没有学习课程的同学，课程数量要与之一致
select * from student a
inner join sc b
on a.sid=b.sid
where b.sid not in (select sid from sc where cid not in
( select cid from sc where sid =01)) and b.sid!=01
group by b.sid
having count(1)= (select count(cid) from sc where sid =01)
- 查询没学过"张三"老师讲授的任一门课程的学生姓名
思路：查询学过「张三」老师授课的同学的信息,取反
select * from student
where sid not in
(select a.sid from student a
inner join sc b
inner join course c
inner join teacher d
on a.sid=b.sid and b.cid=c.cid and c.tid= d.tid
where tname='张三')
- 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
思路：先查出有两门不及格的同学的学号，在与sc,student表关联，最后分组求出平均成绩
#查出有两门不及格的同学的学号
select sid from sc
where score<60
group by sid
having count(1)>1;
select a.sid, b.sname,avg(score)
from sc a
left join student b
on a.sid= b.sid
inner join(
select sid from sc
where score<60
group by sid
having count(1)>1) c
on c.sid= a.sid
group by a.sid ;
- 检索" 01 "课程分数小于 60，按分数降序排列的学生信息
思路：找到01课程的学生信息，筛选分数60分以下的
select a.*,b.score from student a
inner join sc b
on a.sid=b.sid
where cid=01 and score<60
order by b.score desc;
- 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
思路：分组，求平均，排序
select a.*, avg_score from sc a
left join
(select sid,avg(score) as avg_score from sc
group by sid) b
on a.sid =b.sid
order by avg_score desc;
-
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
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
思路：course 和sc表连接，考察条件计数
SELECT a.cid as 课程ID,a.cname as 课程name,
AVG(score) as 平均分 ,
MAX(score) as 最高分,
MIN(score) as 最低分,
SUM(case WHEN b.score>=60 then 1 ELSE 0 END )/count(a.CId) as 及格率,
SUM(case WHEN b.score>=70 and b.score<80 then 1 ELSE 0 END )/count(a.CId) as 中等率,
SUM(case WHEN b.score>=80 and b.score<90 then 1 ELSE 0 END )/count(a.CId) as 优良率,
SUM(case WHEN b.score>=90 then 1 ELSE 0 END )/count(a.CId) as 优秀率
FROM course a
INNER JOIN sc b
ON a.CId=b.CId
GROUP BY a.CId
ORDER BY COUNT(a.CId),a.CId
- 按各科成绩进行排序，并显示排名， Score 重复时继续排名
提示：mysql变量考察
SELECT *,@rank:=@rank+1 as rn
from sc,(SELECT @rank:=0) as c
ORDER BY score DESC;
15.1 按各科成绩进行排序，并显示排名， Score 重复时合并名次
SELECT *,case WHEN @s=score then @rank
WHEN @s:=score then @rank:=@rank+1
end as rn
from sc,(SELECT @rank:=0,@s:=NULL) as c
ORDER BY score DESC;
- 查询学生的总成绩，并进行排名，总分重复时保留名次空缺
SELECT a.sid,a.sum_score,@rank:=if(@s=sum_score,'',@rank+1) as rank,
@s:=sum_score
FROM
(SELECT sid, sum(score) as sum_score
FROM sc
GROUP BY sid
ORDER BY sum_score DESC) a,
(SELECT @rank:=0,@s:=NULL) b;
16.1 查询学生的总成绩，并进行排名，总分重复时不保留名次空缺
SELECT a.sid,a.sum_score,@rank:=@rank+1 as rank
FROM
(SELECT sid, sum(score) as sum_score
FROM sc
GROUP BY sid
ORDER BY sum_score DESC) a,
(SELECT @rank:=0) b;
- 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]，[60-0] 及所占百分比
SELECT a.cid, cname,
CONCAT(sum(CASE WHEN score<60 THEN 1 ELSE 0 END)/count(a.CId)*100,'%') as '[0-60]',
CONCAT(sum(CASE WHEN score>=60 and score<70 THEN 1 ELSE 0 END)/count(a.CId)*100,'%' )as '[70-60]',
CONCAT(sum(CASE WHEN score>=70 and score<85 THEN 1 ELSE 0 END)/count(a.CId)*100,'%' )as '[85-70]',
CONCAT(sum(CASE WHEN score>=85 and score<100 THEN 1 ELSE 0 END)/count(a.CId)*100,'%') as '[100-85]'
from course a
INNER JOIN sc b
ON a.cid=b.cid
GROUP BY a.cid;
- 查询各科成绩前三名的记录***
SELECT a.* from sc a
WHERE ( SELECT count(1) FROM sc b WHERE a.cid=b.cid AND a.score< b.score) <3
ORDER BY a.cid desc,a.sid desc;
- 查询每门课程被选修的学生数
SELECT cid,count(1) as cons
from sc
GROUP BY CId;
- 查询出只选修两门课程的学生学号和姓名
SELECT a.SId,b.sname
from sc a
LEFT JOIN student b
ON a.SId= b.SId
GROUP BY a.SId,b.Sname
HAVING COUNT(1)=2
- 查询男生、女生人数
SELECT ssex,count(1) from student
GROUP BY ssex;
- 查询名字中含有「风」字的学生信息
SELECT * FROM student
where Sname LIKE'%风%';
- 查询同名同性学生名单，并统计同名人数
SELECT a.sname,count(1) from student a,
student b
WHERE a.sid != b.SId and a.Sname= b.Sname AND a.Ssex= b.Ssex;
- 查询 1990 年出生的学生名单
SELECT * from student
where YEAR(sage)='1990';
- 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 cid,avg(score) as avg_score from sc
GROUP BY CId
ORDER BY avg_score DESC ,Cid ASC;
- 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,sname,avg(score) as avg_score from sc a
INNER JOIN student b
ON a.sid=b.SId
GROUP BY a.SId
HAVING avg_score>=85;
- 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 a
INNER JOIN sc b
INNER JOIN course c
ON a.SId= b.SId AND b.CId= c.cid
WHERE c.Cname ='数学' AND b.score<60;
- 查询所有学生的课程及分数情况（存在学生没成绩，没选课的情况）
SELECT a.SId,b.score from student a
left JOIN sc b
on a.sid =b.sid
- 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 sname,cname,score from student a
INNER JOIN sc b
INNER JOIN course c
ON a.sid=b.SId AND b.cid= c.CId
where b.score >70;
- 查询不及格的课程
SELECT a.* from course a
where a.CId IN(
SELECT cid from sc WHERE score<60);
- 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 a.sid ,sname from student a
where sid IN(SELECT sid from sc
WHERE cid='01' AND score>=80)
- 求每门课程的学生人数
SELECT cid,count(1) from sc
GROUP BY cid;
- 成绩不重复，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
SELECT a.*,max(score)from student a
left JOIN sc b
ON a.sid=b.SId
LEFT JOIN course c
ON b.CId =c.CId
LEFT JOIN teacher d
ON c.TId= d.TId
WHERE tname ='张三';
- 成绩有重复的情况下，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**
SELECT *FROM
(SELECT m.*,CASE WHEN @so=score then @rank
WHEN @so:=score THEN @rank:=@rank+1 end as rn
FROM
(SELECT a.*,b.score,d.tname from student a
left JOIN sc b
ON a.sid=b.SId
LEFT JOIN course c
ON b.CId =c.CId
LEFT JOIN teacher d
ON c.TId= d.TId
WHERE tname ='张三'
ORDER BY b.score DESC) m ,
(SELECT @rank:=0,@so:=NULL) n) s
WHERE rn=1
- 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
SELECT a.* from sc a
INNER JOIN sc b
ON a.SId= b.SId
WHERE a.cid!=b.CId and a.score=b.score
GROUP BY a.SId,a.CId;
- 查询每门课程成绩最好的前两名**
SELECT a.* from sc a
WHERE ( SELECT count(1) FROM sc b
WHERE a.cid=b.cid AND a.score< b.score) <2
ORDER BY a.cid DESC,a.sid DESC;
- 统计每门课程的学生选修人数（超过 5 人的课程才统计）
SELECT cid, count(1) FROM sc
GROUP BY CId
HAVING COUNT(1)>5;
- 检索至少选修两门课程的学生学号
SELECT sid from sc
GROUP BY SId
Having count(1)>=2;
- 查询选修了全部课程的学生信息
SELECT sid from sc
GROUP BY SId
Having count(1)=3;
- 查询各学生的年龄，只按年份来算
SELECT Sid,Sname,YEAR(now())-YEAR(sage) AS age
FROM student
SELECT Sid,Sname,ROUND(DATEDIFF(NOW(),Sage)/356) AS age
FROM student
- 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一
select *，TIMESTAMPDIFF(year,Sage,NOW()) age from student；
- 查询本周过生日的学生
select * from student
where WEEK(sage)= week(now());
- 查询下周过生日的学生
select * ,WEEK(sage) from student
where WEEK(sage)= week(now())+1;
- 查询本月过生日的学生
select * ,MONTH(sage) from student
where MONTH(sage)= MONTH(now());
- 查询下月过生日的学生
select * ,MONTH(sage) from student
where MONTH(sage)= MONTH(now())+1;