-- 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
-- 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
-- 7、查询学过"张三"老师授课的同学的信息
方法二：
-- 8、查询没学过"张三"老师授课的同学的信息
-- 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
-- 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
-- 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
-- 28、查询男生、女生人数
-- 42、查询每门课程成绩最好的前两名
-- 35、查询所有学生的课程及分数情况
--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 c.*,a.s_score as 01课程score,b.s_score as 02课程score from
score a,score b
left join student c
on b.s_id = c.s_id
where a.s_id = b.s_id and a.c_id = '01' and b.c_id = '02' and a.s_score >b.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课程,c.s_score as 02课程 from student a
join score b
on a.s_id=b.s_id and b.c_id = '01'
left join score c
on b.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 a.s_id,a.s_name,round(avg(b.s_score),2) as 平均成绩 from student a
join score b
on a.s_id = b.s_id
group by b.s_id having 平均成绩 >= 60
备注：round[avg(成绩),1]里,round是四舍五入函数，1代表保留1位小数
-- 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. ,round(avg(a.s_score),2) as 平均成绩 from
student b
left join score a on b.s_id = a.s_id group by a.s_id having 平均成绩 <60
union
select b. ,0 as 平衡成绩 from student b where b.s_id not in (select 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 选课总数 ,sum(b.s_score) as 总分 from student a
left join score b
on a.s_id = b.s_id group by s_id
-- 6、查询"李"姓老师的数量
select count(*) as 李姓老师数量 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.c_id from course c
join teacher d on c.t_id = d.t_id where d.t_name = '张三')
-- 8、查询没学过"张三"老师授课的同学的信息
select a.* from student a left join score b on a.s_id = b.s_id 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'))) group by a.s_id
-- 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 * from student where s_id in
(select a.s_id from score a join score b on a.s_id = b.s_id
where a.c_id = '01' and b.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 * from student where s_id in
(select s_id from score where c_id = '01' )
and 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
select * from student where s_id not in
(select s_id from score group by s_id having count(c_id) = 3)
-- 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 a.* from student a left join score b
on a.s_id = b.s_id where b.c_id in
(select c_id from score where s_id = '01') and a.s_id != '01'
注意：distinct是去重的
-- 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 * from student where s_id in
(select s_id from score group by s_id having count(c_id) =
(select count(c_id) from score where s_id = '01') and s_id not in
(select s_id from score where c_id not in
(select c_id from score where s_id = '01')) and s_id != '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 s_name from student where s_id not in
(select s_id from score where c_id in
(select c_id from course where t_id in
(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 ,b.s_name,round(avg(a.s_score),2) as 平均成绩 from score a
left join student b on a.s_id = b.s_id
where s_score <60 group by s_id having count(1) >=2
或者试试
select a.s_id ,b.s_name,round(avg(a.s_score),2) as 平均成绩 from score a
left join student b on a.s_id = b.s_id
where a.s_score <60 group by a.s_id having count(*) >=2
-- 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
left join score b on a.s_id = b.s_id
where 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_name ,
sum(case when b.c_id = '01' then s_score else null end ) as 语文,
sum(case when b.c_id = '02' then s_score else null end ) as 数学,
sum(case when b.c_id = '03' then s_score else null end ) as 英语,
round(avg(s_score),2) as 平均成绩
from student a left join score b on a.s_id = b.s_id group by a.s_name
order by 平均成绩 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 b.c_id,b.c_name,
max(a.s_score) as 最高分,
min(a.s_score) as 最低分,
round(avg(a.s_score),2) as 平均分,
round(sum(case when a.s_score>= 60 then 1 else 0 end)/count(s_id),2) as 及格率 ,
round(sum(case when a.s_score>= 70 and a.s_score <80 then 1 else 0 end)/count(s_id),2) as 中等率,
round(sum(case when a.s_score>= 80 and a.s_score <90 then 1 else 0 end)/count(s_id),2) as 优良率,
round(sum(case when a.s_score>= 90 then 1 else 0 end)/count(s_id),2) as 优秀率
from score a
left join course b
on a.c_id = b.c_id group by b.c_id
-- 19、按各科成绩进行排序，并显示排名
第一种：
set @pre_c_id:= '01'
set @rank:=0
select tb2.s_id ,tb2.c_id,tb2.s_score,tb2.排名 from
(select *,(case when tb1.c_id = @pre_c_id then @rank:=@rank+1 else @rank:=1 end) as 排名,
(case when @pre_c_id = tb1.c_id then @pre_c_id else @pre_c_id:=tb1.c_id end ) as pre_c_id
from
(select * from score order by c_id,s_score desc) tb1 )tb2
如果看不懂用第二种方法：
SELECT a.c_id,a.s_id,a.s_score,COUNT(b.s_score)+1 AS 排名
FROM score a LEFT JOIN score b ON a.s_score<b.s_score AND a.c_id = b.c_id
GROUP BY a.c_id,a.s_id,a.s_score ORDER BY a.c_id,排名,a.s_id ASC
-- 20、查询学生的总成绩并进行排名
set @rank:=0
select * ,(@rank:=@rank+1) as rank from
(select s_id ,sum(s_score) as 总成绩 from score
group by s_id order by 总成绩 desc) tb1
-- 21、查询不同老师所教不同课程平均分从高到低显示
select a.c_id, d.t_name,round(avg(a.s_score)) as 平均分 from score a
left join student b on a.s_id = b.s_id
left join course c on a.c_id = c.c_id
left join teacher d on c.t_id = d.t_id group by a.c_id
order by 平均分 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
set @pre_c_id:= '01'
set @rank:=0
select b.s_name,tb2.s_id ,tb2.c_id,tb2.s_score,tb2.排名 from
(select *,(case when tb1.c_id = @pre_c_id then @rank:=@rank+1 else @rank:=1 end) as 排名,
(case when @pre_c_id = tb1.c_id then @pre_c_id else @pre_c_id:=tb1.c_id end ) as pre_c_id
from
(select * from score order by c_id,s_score desc) tb1 )tb2 join student b on tb2.s_id = b.s_id where 排名 = 2 or 排名 =3
-- 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
select b.c_id,b.c_name ,
sum(case when a.s_score >=85 then 1 else 0 end) as 100-85 ,
concat(round(100 sum(case when a.s_score >=85 then 1 else 0 end)/count( ),2), '%') as 百分比,
sum(case when a.s_score <85 and a.s_score >=70 then 1 else 0 end) as 85-70 ,
concat(round(100 sum(case when a.s_score <85 and a.s_score >=70 then 1 else 0 end)/count( ),2),'%') as 百分比,
sum(case when a.s_score <70 and a.s_score >=60 then 1 else 0 end) as 70-60 ,
concat(round(100 sum(case when a.s_score <70 and a.s_score >=60 then 1 else 0 end)/count( ),2) ,'%')as 百分比,
sum(case when a.s_score <60 and a.s_score >=0 then 1 else 0 end) as 60-0 ,
concat(round(100 sum(case when a.s_score <60 and a.s_score >=0 then 1
else 0 end)/count( ),2),'%') as 百分比
from score a left join course b on a.c_id = b.c_id group by b.c_id
-- 24、查询学生平均成绩及其名次
select tb1.*,(@rank:=@rank +1 ) as rank from
(select s_id ,round(avg(s_score),2) as 平均成绩 from score
group by s_id order by 平均成绩 desc) tb1,(select @rank:=0) b
-- 25、查询各科成绩前三名的记录
set @pre_c_id:= '01'
set @rank:=0
select b.s_name,tb2.s_id ,tb2.c_id,tb2.s_score,tb2.排名 from
(select *,(case when tb1.c_id = @pre_c_id then @rank:=@rank+1 else @rank:=1 end) as 排名,
(case when @pre_c_id = tb1.c_id then @pre_c_id else @pre_c_id:=tb1.c_id end ) as pre_c_id
from
(select * from score order by c_id,s_score desc) tb1 )tb2 join student b on tb2.s_id = b.s_id where 排名 <4
-- 26、查询每门课程被选修的学生数
select c_id ,count(s_id) as 选修人数 from score group by c_id
-- 27、查询出只有两门课程的全部学生的学号和姓名
select a.s_id ,b.s_name from score a left join student b on a.s_id = b.s_id group by s_id having count(*) = 2
-- 28、查询男生、女生人数
select sum(case s_sex when '男' then 1 else 0 end) as 男生人数,
sum(case s_sex when '女' then 1 else 0 end) as 女生人数 from student
-- 29、查询名字中含有"风"字的学生信息
select * from student where s_name like '%风%'
-- 30、查询同名同性学生名单，并统计同名人数
--略，不想写
-- 31、查询1990年出生的学生名单
select * from student where s_birth like '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 c_id ,round(avg(s_score),2) as 平均成绩 from score group by c_id order by 平均成绩 desc, c_id 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.s_id,b.s_name ,round(avg(s_score),2) as 平均成绩 from score a
left join student b on a.s_id = b.s_id group by a.s_id having 平均成绩>=85
-- 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 b.s_name ,a.s_score from score a
left join student b on a.s_id = b.s_id
where a.c_id=(select c_id from course where c_name = '数学')and a.s_score <60
-- 35、查询所有学生的课程及分数情况；
select b.s_name,
sum(case when a.c_id = '01' then a.s_score else null end) as 语文,
sum(case when a.c_id = '02' then a.s_score else null end) as 数学,
sum(case when a.c_id = '03' then a.s_score else null end) as 英语
from score a right join student b on a.s_id = b.s_id group by b.s_name
-- 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 b.s_name,
sum(case when a.c_id = '01' then a.s_score else null end) as 语文,
sum(case when a.c_id = '02' then a.s_score else null end) as 数学,
sum(case when a.c_id = '03' then a.s_score else null end) as 英语
from score a right join student b on a.s_id = b.s_id group by b.s_name having 语文>= 70 or 数学>= 70 or 英语>= 70
-- 37、查询不及格的课程
select a.s_id,a.c_id,b.c_name,a.s_score from score a
left join course b on a.c_id = b.c_id where a.s_score<60
--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 a.s_id,b.s_name from score a left join student b on a.s_id = b.s_id where a.c_id = '01' and a.s_score>=80
-- 39、求每门课程的学生人数
select c_id,count(*) as 学生人数 from score group by c_id
-- 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
select a.*,b.c_id,max(b.s_score) as 最高成绩 from student a
right join score b on a.s_id = b.s_id
group by b.c_id
having b.c_id = (select c_id from course
where t_id = (select t_id from teacher where t_name = '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
--（这题我搞不清题目是什么意思,是指查找学生个体参加了的所有课程的成绩各不相同的那个学生信息呢？还是所有课程之间做对比呢，我更倾向于理解为前者）
--理解为前者的写法
select * from
(select * from score group by s_id,s_score) tb1
group by s_id having count(*) = 1
--理解为后者的写法
select distinct a.s_id,a.c_id,b.s_score from score a,score b where a.c_id != b.c_id and a.s_score = b.s_score
-- 42、查询每门课程成绩最好的前两名
set @pre_c_id:= '01'
set @rank:=0
select tb2.s_id ,tb2.c_id,tb2.s_score from
(select *,(case when tb1.c_id = @pre_c_id then @rank:=@rank+1 else @rank:=1 end) as 排名,
(case when @pre_c_id = tb1.c_id then @pre_c_id else @pre_c_id:=tb1.c_id end ) as pre_c_id
from
(select * from score order by c_id,s_score desc) tb1 )tb2
join student b on tb2.s_id = b.s_id where 排名 <3
-- 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，若人相同，按课程号升序排列
select c_id ,count(*) as 选修人数 from score group by c_id having 选修人数>5 order by 选修人数 desc , c_id asc
-- 44、检索至少选修两门课程的学生学号
select s_id from score group by s_id having count(*) >= 2
-- 45、查询选修了全部课程的学生信息
select * from student where s_id in
(select s_id from score group by s_id having count(*) = 3)
--46、查询各学生的年龄
select s_name ,(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
-- 47、查询本周过生日的学生
---(实现得并不完全，因为例如出生月日为‘01-01’在每一年可能会输入不同周）
select * from student where week(date_format(s_birth,'%m%d'))=week(date_format(now(),'%m%d'))
-- 48、查询下周过生日的学生
select * from student
where week(date_format(s_birth,'%m%d'))=week(date_format(date_add(now(),interval 7-dayofweek(now())+1 day),'%m%d'))
-- 49、查询本月过生日的学生
select * from student where date_format(s_birth,'%m') = date_format(now(),'%m')
-- 50、查询下月过生日的学生
select * from student where date_format(s_birth,'%m') = date_format(date_add(now(),interval 1 month),'%m')
Hello，写的语言格式有些丑
练习题目：
3、多表连接（等值连接）
①案例1 ：查询员工名、部门名
②为表起别名
# ③添加筛选条件
# 案例：查询 工资>5000 的工种名和员工名、工资
④添加分组和筛选
#01 案例：查询每个部门的员工个数和部门名
⑤排序
#01 案例：查询每个部门的员工个数和部门名
⑥ 三表连接
# 案例：查询员工名、部门名和所在城市
4、多表连接（等值连接）练习
传统模式的多表连接
1. 显示所有员工的姓名，部门号和部门名称。
2. 查询90 号部门员工的job_id 和90 号部门的location_id
3. 选择所有有奖金的员工的last_name , department_name , location_id , city
----------- 三表连查
4. 选择city 在Toronto 工作的员工的
last_name , job_id , department_id , department_name ----------- 三表连查
5. 查询每个工种、每个部门的部门名、工种名和最低工资 ----------- 三表连查
6. 查询每个国家下的部门个数大于2 的国家编号
5、非等值查询
2.非等值连接
#案例1：查询员工的工资以及对应的工资级别
#案例2：查询名字中第三个字符为a，第五个字符为e的员工的工资以及对应的工资级别
6、内连接
#案例1 ：查询员工名、部门名
案例2：查询有奖金的员工名、部门名
案例3：查询城市名、员工名和部门名
9、练习
一、查询编号>3的女神的男朋友信息，如果有则列出详细，如果没有，用null填充
#二、查询哪个城市没有部门
三、查询部门名为SAL或IT的员工信息
#四、选择指定员工的姓名，员工号，以及他的管理者的姓名和员工号，结果类似于下面的格式
/*
employees Emp# manager Mgr#
kochhar 101 king
100
*/
10、单行子查询
案例1：谁的工资比Abel高
①查询Abel的工资
②查询员工的信息满足工资>①的结果
案例2：题目：返回job_id与141号员工相同，salary比143号员工多的员工 的姓名，job_id 和工资
①查询141的job_id
②查询143的salary
③查询 姓名，job_id 和工资，满足job_id=①并且salary>②
案例3：返回公司工资最少的员工的last_name,job_id和salary
①查询最低工资
②查询员工的last_name,job_id和salary满足 salary=①
案例4：查询最低工资大于50号部门最低工资的部门id和其最低工资
①查询50号部门的最低工资
②查询每个部门的最低工资
③筛选最低工资>①
11、多行子查询
二、多行子查询
案例1：返回location_id是1400或1700的部门中的所有员工姓名
①查询location_id是1400或1700的部门编号
②查询department_id满足①结果的员工姓名
案例2：返回其它部门中比job_id为‘IT_PROG’部门任意工资低的员工的员
工号、姓名、job_id 以及salary
①查询job_id为‘IT_PROG’部门工资
②返回其它部门中，工资<any ①的结果
题目：返回其它部门中比job_id为‘IT_PROG’部门所有工资都低的员工
#的员工号、姓名、job_id 以及salary
12、子查询练习题
#1. 查询和Zlotkey 相同部门的员工姓名和工资
#2. 查询工资比公司平均工资高的员工的员工号，姓名和工资。
#①查询公司平均工资
② 查询工资>①的员工的员工号，姓名和工资。
#3. 查询各部门中工资比本部门平均工资高的员工的员工号, 姓名和工资
①查询各部门的平均工资
②查询员工的员工号, 姓名和工资，满足本部门并且工资>①
4. 查询姓名中包含字母u 的员工在相同部门的员工的员工号和姓名
①查询姓名中包含字母u的员工的部门
② 部门=①的员工的员工号和姓名
5. 查询在部门的location_id 为1700 的部门工作的员工的员工号
①查询loaction_id =1700的部门编号
② 查询员工号，满足部门号=①
#6. 查询管理者是King 的员工姓名和工资
①查询员工名是king的编号
#② 查询员工姓名和工资，领导的编号=①
#7. 查询工资最高的员工的姓名，要求first_name 和last_name 显示为一列，列名为 姓. 名
①查询最高工资
②查询姓名，工资=①
14、子查询巩固练习
# 1 、查询工资最低的员工信息
#①查询公司的最低工资
②查询员工信息，满足 salary=①
2. 查询平均工资最低的部门信息
①查询每个部门的平均工资
②查询①结果中avg(salary) 字段中的最低值
# ③查询部门编号，满足平均工资= ②结果
④查询部门信息，满足 department_id= ③
3*. 查询平均工资最低的部门信息和该部门的平均工资
4. 查询平均工资最高的 job 信息
①查询每个job的平均工资
②查询①结果中的 avg(salary)的最高值
③查询每个工种的平均工资，满足 平均工资=②
④工种表和③连接 ， 查询平均工资最高的 job 信息
# 5. 查询平均工资高于公司平均工资的部门有哪些?
#①查询公司的平均工资
②查询每个部门的平均工资，并且平均工资>①
6. 查询平均工资最高的部门的 manager 的详细信息:
①查询平均工资最高的部门编号
②查询部门编号=①的manager的详细信息
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