mysql学习训练记录及笔记（一）

写这篇的缘由是因为感觉本地保存容易误删，存到云盘中，还要下载打开，麻烦，因此记录在博客中

I、建表语句

--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);

View Code

II、sql语言训练

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,
    c.s_score
from
    student a join score b on
    a.s_id = b.s_id
    and b.c_id='01'
    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;

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, c.s_score
from student a join score b on a.s_id =b.s_id and b.c_id ='01'
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 a.s_id,a.s_name, avg(b.s_score) from student a join score b on a.s_id = b.s_id group by a.s_id,a.s_name having avg(b.s_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 a.s_id,a.s_name, avg(b.s_score) from student a join score b on a.s_id = b.s_id group by a.s_id,a.s_name having avg(b.s_score)<60
union
select a.s_id,a.s_name,0  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 t1.s_id,t1.s_name,count(t2.c_id),sum(t2.s_score) from student t1 join score t2 on t1.s_id = t2.s_id
group by t1.s_id,t1.s_name ;

6、-- 查询"李"姓老师的数量 

select count(1) 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 join course c on b.c_id = c.c_id 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 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'
        )
    ));

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 a 
    where a.s_id in (
    select a.s_id from score a join score b on a.s_id=b.s_id and 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 a.s_id from score a where a.c_id = '01' and a.s_id not in (
         select b.s_id from score b where b.c_id = '02')
     );

11、-- 查询没有学全所有课程的同学的信息 

select * from
    student a
    where a.s_id not in (
    select s_id from score b group by b.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 s_id from score where  c_id in (select c_id from score where 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、

select * from student
where s_id in
(select s_id from score group by s_id having group_concat(c_id order by c_id) = 
(select group_concat(c_id order by c_id) from score  where 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 t1.s_name from student t1 where t1.s_id not in
(select s_id from score t2 where t2.c_id in (select c_id from course a join  teacher b on a.t_id=b.t_id 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 t1.s_id ,t1.s_name,avg(t2.s_score) from student t1 join score t2 on t1.s_id=t2.s_id where t2.s_score<60 group by t1.s_id having count(t2.s_score)>1;

-- 16、检索"01"课程分数小于60，按分数降序排列的学生信息

select * from student t1 join score t2 on t1.s_id = t2.s_id where t2.s_score < 60 and t2.c_id = '01' order by t2.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 s_id,(select s_score from score where t1.s_id=s_id and c_id='01') as a,
(select s_score from score where t1.s_id=s_id and c_id='02') as b,
(select s_score from score where t1.s_id= s_id and c_id='03') as c,
avg(s_score)
from score t1 group by s_id order by avg(s_score) 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 score.c_id,course.c_name,max(s_score),min(s_score),avg(s_score),
(sum(s_score>=60)/count(s_score)),
(sum(case when  s_score between 70 and 80 then 1 else 0 end)/count(s_score)),
(sum(case when  s_score between 80 and 90 then 1 else 0 end)/count(s_score)),
(sum(case when  s_score >=90 then 1 else 0 end)/count(s_score))
from score join course on score.c_id = course.c_id
group by c_id

19、按各科成绩进行排序，并显示排名

select @i:= @i + 1,s_score,s_id,c_id
from score,(select @i:=0) as a order by s_score desc

20、查询学生的总成绩并进行排名

select @i:=@i+1,sum_score,s_id
from (
select s_id,sum(s_score) as sum_score
from score group by s_id order by sum(s_score) desc
) b,(select @i:=0) a

III、总结一下，前20题涉及知识点包括

1、各语句执行顺序：

sql语句顺序

<SELECT clause> [<FROM clause>] [<WHERE clause>] [<GROUP BY clause>] [<HAVING clause>] [<ORDER BY clause>] [<LIMIT clause>] 

数据库底层执行顺序

 2、子查询

 a、   where型子查询：指把内部查询的结果作为外层查询的比较条件。
 b、   from型子查询：把内层的查询结果当成临时表，供外层sql再次查询。
 c、 in子查询：内层查询语句仅返回一个数据列，这个数据列的值将供外层查询语句进行比较。
 d、 exists子查询：把外层的查询结果，拿到内层，看内层是否成立，简单来说后面的返回true,外层（也就是前面的语句）才会执行，否则不执行。
 e、 any子查询：只要满足内层子查询中的任意一个比较条件，就返回一个结果作为外层查询条件。
 f、  all子查询：内层子查询返回的结果需同时满足所有内层查询条件。
 g、 比较运算符子查询：子查询中可以使用的比较运算符如 “>” “<” “= ” “!=”

3、group_concat连接列数据，需要配合groupby使用

4、@符号使用，声明用户变量

oracle中有rownum这个伪列，自增序号，但是mysql中没有，因此借用@进行递增赋值

注意需要先进行子查询排序，再补加序列号，因为@i：=@i+1赋值语句执行在order by之前

在from中增加select @i:=0,是进行初始赋值

5、case when

通常使用方法为case when xxx then [value] else [value] end