表名和字段
–1.学生表
Student(s_id,s_name,s_birth,s_sex) --学生编号,学生姓名, 出生年月,学生性别
–2.课程表
Course(c_id,c_name,t_id) – --课程编号, 课程名称, 教师编号
–3.教师表
Teacher(t_id,t_name) --教师编号,教师姓名
–4.成绩表
Score(s_id,c_id,s_score) --学生编号,课程编号,分数

–建表
–学生表
CREATE TABLE Student(
s_id VARCHAR(20),
s_name VARCHAR(20) NOT NULL DEFAULT ‘’,
s_birth VARCHAR(20) NOT NULL DEFAULT ‘’,
s_sex VARCHAR(10) NOT NULL DEFAULT ‘’,
PRIMARY KEY(s_id)
);
–课程表
CREATE TABLE Course(
c_id VARCHAR(20),
c_name VARCHAR(20) NOT NULL DEFAULT ‘’,
t_id VARCHAR(20) NOT NULL,
PRIMARY KEY(c_id)
);
–教师表
CREATE TABLE Teacher(
t_id VARCHAR(20),
t_name VARCHAR(20) NOT NULL DEFAULT ‘’,
PRIMARY KEY(t_id)
);
–成绩表
CREATE TABLE Score(
s_id VARCHAR(20),
c_id VARCHAR(20),
s_score INT(3),
PRIMARY KEY(s_id,c_id)
);
–插入学生表测试数据
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’);
–课程表测试数据
insert into Course values(‘01’ , ‘语文’ , ‘02’);
insert into Course values(‘02’ , ‘数学’ , ‘01’);
insert into Course values(‘03’ , ‘英语’ , ‘03’);

–教师表测试数据
insert into Teacher values(‘01’ , ‘张三’);
insert into Teacher values(‘02’ , ‘李四’);
insert into Teacher values(‘03’ , ‘王五’);

–成绩表测试数据
insert into Score values(‘01’ , ‘01’ , 80);
insert into Score values(‘01’ , ‘02’ , 90);
insert into Score values(‘01’ , ‘03’ , 99);
insert into Score values(‘02’ , ‘01’ , 70);
insert into Score values(‘02’ , ‘02’ , 60);
insert into Score values(‘02’ , ‘03’ , 80);
insert into Score values(‘03’ , ‘01’ , 80);
insert into Score values(‘03’ , ‘02’ , 80);
insert into Score values(‘03’ , ‘03’ , 80);
insert into Score values(‘04’ , ‘01’ , 50);
insert into Score values(‘04’ , ‘02’ , 30);
insert into Score values(‘04’ , ‘03’ , 20);
insert into Score values(‘05’ , ‘01’ , 76);
insert into Score values(‘05’ , ‘02’ , 87);
insert into Score values(‘06’ , ‘01’ , 31);
insert into Score values(‘06’ , ‘03’ , 34);
insert into Score values(‘07’ , ‘02’ , 89);
insert into Score 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

select a.* ,b.s_score as 01_score,c.s_score as 02_score from
student a
join score b on a.s_id=b.s_id and b.c_id=‘01’
left join score c on a.s_id=c.s_id and c.c_id=‘02’ or c.c_id = NULL where b.s_score>c.s_score

–也可以这样写
select a.*,b.s_score as 01_score,c.s_score as 02_score from student a,score b,score c
where a.s_id=b.s_id
and a.s_id=c.s_id
and b.c_id=‘01’
and c.c_id=‘02’
and b.s_score>c.s_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

select a.* ,b.s_score as 01_score,c.s_score as 02_score from
student a left join score b on a.s_id=b.s_id and b.c_id=‘01’ or b.c_id=NULL
join score c on a.s_id=c.s_id and c.c_id=‘02’ where b.s_score<c.s_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 b.s_id,b.s_name,ROUND(AVG(a.s_score),2) as avg_score from
student b
join score a on b.s_id = a.s_id
GROUP BY b.s_id,b.s_name HAVING avg_score >=60;

– 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
– (包括有成绩的和无成绩的)

select b.s_id,b.s_name,ROUND(AVG(a.s_score),2) as avg_score from
student b
left join score a on b.s_id = a.s_id
GROUP BY b.s_id,b.s_name HAVING avg_score <60
union
select a.s_id,a.s_name,0 as avg_score from
student a
where a.s_id not in (
select distinct s_id from score);

– 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
select a.s_id,a.s_name,count(b.c_id) as sum_course,sum(b.s_score) as sum_score from
student a
left join score b on a.s_id=b.s_id
GROUP BY a.s_id,a.s_name;

– 6、查询"李"姓老师的数量
select count(t_id) from teacher where t_name like ‘李%’;

– 7、查询学过"张三"老师授课的同学的信息
select a.* from
student a
join score b on a.s_id=b.s_id where b.c_id in(
select c_id from course where t_id =(
select t_id from teacher where t_name = ‘张三’));

– 8、查询没学过"张三"老师授课的同学的信息
select * from
student c
where c.s_id not in(
select a.s_id from student a join score b on a.s_id=b.s_id where b.c_id in(
select a.c_id from course a join teacher b on a.t_id = b.t_id where t_name =‘张三’));
– 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

select a.* from
student a,score b,score c
where a.s_id = b.s_id and a.s_id = c.s_id and b.c_id=‘01’ and c.c_id=‘02’;

– 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

select a.* from
student a
where a.s_id in (select s_id from score where c_id=‘01’ ) and a.s_id not in(select s_id from score where c_id=‘02’)

– 11、查询没有学全所有课程的同学的信息
–@wendiepei的写法
select s.* from student s
left join Score s1 on s1.s_id=s.s_id
group by s.s_id having count(s1.c_id)<(select count() from course)
–@k1051785839的写法
select *
from student
where s_id not in(
select s_id from score t1
group by s_id having count() =(select count(distinct c_id) 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 * from student where s_id in(
select distinct a.s_id from score a where a.c_id in(select a.c_id from score a where a.s_id=‘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
–@ouyang_1993的写法
SELECT
Student.*
FROM
Student
WHERE
s_id IN (SELECT s_id FROM Score GROUP BY s_id HAVING COUNT(s_id) = (
#下面的语句是找到’01’同学学习的课程数
SELECT COUNT(c_id) FROM Score WHERE s_id = ‘01’
)
)
AND s_id NOT IN (
#下面的语句是找到学过‘01’同学没学过的课程，有哪些同学。并排除他们
SELECT s_id FROM Score
WHERE c_id IN(
#下面的语句是找到‘01’同学没学过的课程
SELECT DISTINCT c_id FROM Score
WHERE c_id NOT IN (
#下面的语句是找出‘01’同学学习的课程
SELECT c_id FROM Score WHERE s_id = ‘01’
)
) GROUP BY s_id
) #下面的条件是排除01同学
AND s_id NOT IN (‘01’)
–@k1051785839的写法
SELECT
t3.*
FROM
(
SELECT
s_id,
group_concat(c_id ORDER BY c_id) group1
FROM
score
WHERE
s_id <> ‘01’
GROUP BY
s_id
) t1
INNER JOIN (
SELECT
group_concat(c_id ORDER BY c_id) group2
FROM
score
WHERE
s_id = ‘01’
GROUP BY
s_id
) t2 ON t1.group1 = t2.group2
INNER JOIN student t3 ON t1.s_id = t3.s_id

– 14、查询没学过"张三"老师讲授的任一门课程的学生姓名
select a.s_name from student a where a.s_id not in (
select s_id from score where c_id =
(select c_id from course where t_id =(
select t_id from teacher where t_name = ‘张三’)));

– 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 a.s_id,a.s_name,ROUND(AVG(b.s_score)) from
student a
left join score b on a.s_id = b.s_id
where a.s_id in(
select s_id from score where s_score<60 GROUP BY s_id having count(1)>=2)
GROUP BY a.s_id,a.s_name

– 16、检索"01"课程分数小于60，按分数降序排列的学生信息
select a.*,b.c_id,b.s_score from
student a,score b
where a.s_id = b.s_id and b.c_id=‘01’ and b.s_score<60 ORDER BY b.s_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
select a.s_id,(select s_score from score where s_id=a.s_id and c_id=‘01’) as 语文,
(select s_score from score where s_id=a.s_id and c_id=‘02’) as 数学,
(select s_score from score where s_id=a.s_id and c_id=‘03’) as 英语,
round(avg(s_score),2) as 平均分 from score a GROUP BY a.s_id ORDER BY 平均分 DESC;
–@喝完这杯还有一箱的写法
SELECT a.s_id,MAX(CASE a.c_id WHEN ‘01’ THEN a.s_score END ) 语文,
MAX(CASE a.c_id WHEN ‘02’ THEN a.s_score END ) 数学,
MAX(CASE a.c_id WHEN ‘03’ THEN a.s_score END ) 英语,
avg(a.s_score),b.s_name FROM Score a JOIN Student b ON a.s_id=b.s_id GROUP BY a.s_id ORDER BY 5 DESC
– 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
select a.c_id,b.c_name,MAX(s_score),MIN(s_score),ROUND(AVG(s_score),2),
ROUND(100*(SUM(case when a.s_score>=60 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 及格率,
ROUND(100*(SUM(case when a.s_score>=70 and a.s_score<=80 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 中等率,
ROUND(100*(SUM(case when a.s_score>=80 and a.s_score<=90 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 优良率,
ROUND(100*(SUM(case when a.s_score>=90 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 优秀率
from score a left join course b on a.c_id = b.c_id GROUP BY a.c_id,b.c_name

– 19、按各科成绩进行排序，并显示排名
– mysql没有rank函数
select a.s_id,a.c_id,
@i:=@i +1 as i保留排名,
@k:=(case when @score=a.s_score then @k else @i end) as rank不保留排名,
@score:=a.s_score as score
from (
select s_id,c_id,s_score from score GROUP BY s_id,c_id,s_score ORDER BY s_score DESC
)a,(select @k:=0,@i:=0,@score:=0)s
–@k1051785839的写法
(select * from (select
t1.c_id,
t1.s_score,
(select count(distinct t2.s_score) from score t2 where t2.s_score>=t1.s_score and t2.c_id=‘01’) rank
FROM score t1 where t1.c_id=‘01’
order by t1.s_score desc) t1)
union
(select * from (select
t1.c_id,
t1.s_score,
(select count(distinct t2.s_score) from score t2 where t2.s_score>=t1.s_score and t2.c_id=‘02’) rank
FROM score t1 where t1.c_id=‘02’
order by t1.s_score desc) t2)
union
(select * from (select
t1.c_id,
t1.s_score,
(select count(distinct t2.s_score) from score t2 where t2.s_score>=t1.s_score and t2.c_id=‘03’) rank
FROM score t1 where t1.c_id=‘03’
order by t1.s_score desc) t3)
– 20、查询学生的总成绩并进行排名
select a.s_id,
@i:=@i+1 as i,
@k:=(case when @score=a.sum_score then @k else @i end) as rank,
@score:=a.sum_score as score
from (select s_id,SUM(s_score) as sum_score from score GROUP BY s_id ORDER BY sum_score DESC)a,
(select @k:=0,@i:=0,@score:=0)s

– 21、查询不同老师所教不同课程平均分从高到低显示

select a.t_id,c.t_name,a.c_id,ROUND(avg(s_score),2) as avg_score from course a
	left join score b on a.c_id=b.c_id 
	left join teacher c on a.t_id=c.t_id
	GROUP BY a.c_id,a.t_id,c.t_name ORDER BY avg_score DESC;

		select d.*,c.排名,c.s_score,c.c_id from (
            select a.s_id,a.s_score,a.c_id,@i:=@i+1 as 排名 from score a,(select @i:=0)s where a.c_id='01'  
							ORDER BY a.s_score DESC  
        )c
        left join student d on c.s_id=d.s_id
        where 排名 BETWEEN 2 AND 3
        UNION
        select d.*,c.排名,c.s_score,c.c_id from (
            select a.s_id,a.s_score,a.c_id,@j:=@j+1 as 排名 from score a,(select @j:=0)s where a.c_id='02'  
							ORDER BY a.s_score DESC
        )c
        left join student d on c.s_id=d.s_id
        where 排名 BETWEEN 2 AND 3
        UNION
        select d.*,c.排名,c.s_score,c.c_id from (
            select a.s_id,a.s_score,a.c_id,@k:=@k+1 as 排名 from score a,(select @k:=0)s where a.c_id='03' 
							ORDER BY a.s_score DESC
        )c
        left join student d on c.s_id=d.s_id
        where 排名 BETWEEN 2 AND 3;

	select distinct f.c_name,a.c_id,b.`85-100`,b.百分比,c.`70-85`,c.百分比,d.`60-70`,d.百分比,e.`0-60`,e.百分比 from score a
			left join (select c_id,SUM(case when s_score >85 and s_score <=100 then 1 else 0 end) as `85-100`,
										ROUND(100*(SUM(case when s_score >85 and s_score <=100 then 1 else 0 end)/count(*)),2) as 百分比
							from score GROUP BY c_id)b on a.c_id=b.c_id
			left join (select c_id,SUM(case when s_score >70 and s_score <=85 then 1 else 0 end) as `70-85`,
										ROUND(100*(SUM(case when s_score >70 and s_score <=85 then 1 else 0 end)/count(*)),2) as 百分比
							from score GROUP BY c_id)c on a.c_id=c.c_id
			left join (select c_id,SUM(case when s_score >60 and s_score <=70 then 1 else 0 end) as `60-70`,
										ROUND(100*(SUM(case when s_score >60 and s_score <=70 then 1 else 0 end)/count(*)),2) as 百分比
							from score GROUP BY c_id)d on a.c_id=d.c_id
			left join (select c_id,SUM(case when s_score >=0 and s_score <=60 then 1 else 0 end) as `0-60`,
										ROUND(100*(SUM(case when s_score >=0 and s_score <=60 then 1 else 0 end)/count(*)),2) as 百分比
							from score GROUP BY c_id)e on a.c_id=e.c_id
			left join course f on a.c_id = f.c_id

	select a.s_id,
			@i:=@i+1 as '不保留空缺排名',
			@k:=(case when @avg_score=a.avg_s then @k else @i end) as '保留空缺排名',
			@avg_score:=avg_s as '平均分'
	from (select s_id,ROUND(AVG(s_score),2) as avg_s from score GROUP BY s_id ORDER BY avg_s DESC)a,(select @avg_score:=0,@i:=0,@k:=0)b;

	select c_id,count(s_id) from score a GROUP BY c_id

	select * from student where s_name like '%风%';

	select a.s_name,a.s_sex,count(*) from student a  JOIN 
				student b on a.s_id !=b.s_id and a.s_name = b.s_name and a.s_sex = b.s_sex
	GROUP BY a.s_name,a.s_sex

	select s_name from student where s_birth like '1990%'

select c_id,ROUND(AVG(s_score),2) as avg_score from score GROUP BY c_id ORDER BY avg_score DESC,c_id ASC

select a.s_id,b.s_name,ROUND(avg(a.s_score),2) as avg_score from score a
	left join student b on a.s_id=b.s_id GROUP BY s_id HAVING avg_score>=85

	select a.s_name,b.s_score from score b join student a on a.s_id=b.s_id where b.c_id=(
				select c_id from course where c_name ='数学') and b.s_score<60

	select a.s_id,a.s_name,
				SUM(case c.c_name when '语文' then b.s_score else 0 end) as '语文',
				SUM(case c.c_name when '数学' then b.s_score else 0 end) as '数学',
				SUM(case c.c_name when '英语' then b.s_score else 0 end) as '英语',
				SUM(b.s_score) as  '总分'
	from student a left join score b on a.s_id = b.s_id 
	left join course c on b.c_id = c.c_id 
	GROUP BY a.s_id,a.s_name

	-- 查询老师id	
	select c_id from course c,teacher d where c.t_id=d.t_id and d.t_name='张三'
	-- 查询最高分（可能有相同分数）
	select MAX(s_score) from score where c_id='02'
	-- 查询信息
	select a.*,b.s_score,b.c_id,c.c_name from student a
		LEFT JOIN score b on a.s_id = b.s_id
		LEFT JOIN course c on b.c_id=c.c_id
		where b.c_id =(select c_id from course c,teacher d where c.t_id=d.t_id and d.t_name='张三')
		and b.s_score in (select MAX(s_score) from score where c_id='02')

select s_birth,(DATE_FORMAT(NOW(),'%Y')-DATE_FORMAT(s_birth,'%Y') - 
			(case when DATE_FORMAT(NOW(),'%m%d')>DATE_FORMAT(s_birth,'%m%d') then 0 else 1 end)) as age
	from student;

select WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))

select * from student where MONTH(DATE_FORMAT(NOW(),'%Y%m%d')) =MONTH(s_birth)