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day27 SQL强化和实践

image-20210531085557128

课程目标：练习常见的SQL语句和表结构的设计。

课程概要：

  • SQL强化
  • 表结构设计（博客系统）

1. SQL强化

image-20210531123055185

  1. 根据上图创建 数据库 & 表结构 并 录入数据（可以自行创造数据）
create database day27db default charset utf8 collate utf8_general_ci;
use day27db;

drop database day27db;
drop database IF EXISTS day27db;

利用导入数据库命令：

  • 导入

    mysql -u root -p  day27db < /Users/wupeiqi/day27db.sql

  • 导出

    # 结构+数据
mysqldump -u root -p  day27db > /Users/wupeiqi/day27db2.sql

# 结构
mysqldump -u root -p -d day27db > /Users/wupeiqi/day27db3.sql

create table class(
 cid int not null auto_increment primary key,
    caption varchar(16) not null
)default charset=utf8;

INSERT INTO class VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班');


create table student(
  sid int not null auto_increment primary key,
    gender char(1) not null,
    class_id int not null,
    sname varchar(16) not null,
    constraint fk_student_class foreign key (class_id) references class(cid)
)default charset=utf8;

INSERT INTO student VALUES ('1', '男', '1', '理解'), ('2', '女', '1', '钢蛋'), ('3', '男', '1', '张三'), ('4', '男', '1', '张一'), ('5', '女', '1', '张二'), ('6', '男', '1', '张四'), ('7', '女', '2', '铁锤'), ('8', '男', '2', '李三'), ('9', '男', '2', '李一'), ('10', '女', '2', '李二'), ('11', '男', '2', '李四'), ('12', '女', '3', '如花'), ('13', '男', '3', '刘三'), ('14', '男', '3', '刘一'), ('15', '女', '3', '刘二'), ('16', '男', '3', '刘四');


create table teacher(
  tid int not null auto_increment primary key,
    tname varchar(16) not null
)default charset=utf8;

INSERT INTO `teacher` VALUES ('1', '张磊老师'), ('2', '李平老师'), ('3', '刘海燕老师'), ('4', '朱云海老师'), ('5', '李杰老师');


create table course(
    cid int not null auto_increment primary key,
    cname varchar(16) not null,
    teacher_id int not null,
    constraint fk_course_teacher foreign key (teacher_id) references teacher(tid)
)default charset=utf8;

INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2');


CREATE TABLE `score` (
  `sid` int NOT NULL AUTO_INCREMENT PRIMARY KEY,
  `student_id` int NOT NULL,
  `course_id` int NOT NULL,
  `num` int NOT NULL,
  CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
  CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
) DEFAULT CHARSET=utf8;


INSERT INTO `score` VALUES ('1', '1', '1', '10'), ('2', '1', '2', '9'), ('5', '1', '4', '66'), ('6', '2', '1', '8'), ('8', '2', '3', '68'), ('9', '2', '4', '99'), ('10', '3', '1', '77'), ('11', '3', '2', '66'), ('12', '3', '3', '87'), ('13', '3', '4', '99'), ('14', '4', '1', '79'), ('15', '4', '2', '11'), ('16', '4', '3', '67'), ('17', '4', '4', '100'), ('18', '5', '1', '79'), ('19', '5', '2', '11'), ('20', '5', '3', '67'), ('21', '5', '4', '100'), ('22', '6', '1', '9'), ('23', '6', '2', '100'), ('24', '6', '3', '67'), ('25', '6', '4', '100'), ('26', '7', '1', '9'), ('27', '7', '2', '100'), ('28', '7', '3', '67'), ('29', '7', '4', '88'), ('30', '8', '1', '9'), ('31', '8', '2', '100'), ('32', '8', '3', '67'), ('33', '8', '4', '88'), ('34', '9', '1', '91'), ('35', '9', '2', '88'), ('36', '9', '3', '67'), ('37', '9', '4', '22'), ('38', '10', '1', '90'), ('39', '10', '2', '77'), ('40', '10', '3', '43'), ('41', '10', '4', '87'), ('42', '11', '1', '90'), ('43', '11', '2', '77'), ('44', '11', '3', '43'), ('45', '11', '4', '87'), ('46', '12', '1', '90'), ('47', '12', '2', '77'), ('48', '12', '3', '43'), ('49', '12', '4', '87'), ('52', '13', '3', '87');
  1. 创建用户 luffy 并赋予此数据库的所有权限。
create user 'luffy'@'%' identified by 'root123';
grant all privileges on day27db.* TO 'luffy'@'%';
flush privileges;
  1. 查询姓“李”的老师的个数。
select * from teacher where tname like "李%";
  1. 查询姓“张”的学生名单。
select * from student where sname like "张%";
  1. 查询男生、女生的人数。
select gender,count(1) from student group by gender;
  1. 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;
select sname,count(1) from student group by sname having count(1) > 1;
  1. 查询 “三年二班” 的所有学生。
select * from student left join class on student.class_id = class.cid where class.caption="三年二班";
  1. 查询 每个 班级的 班级名称、班级人数。
select class_id,count(1) from student group by class_id;

select class.caption,count(1) from student left join class on student.class_id = class.cid group by class.caption;
  1. 查询成绩小于60分的同学的学号、姓名、成绩、课程名称。
select * from score where num <60;

select 
 student.sid,
 student.sname,
 score.num,
 course.cname 
from 
 score 
 left join student on score.student_id=student.sid 
 left join course on score.course_id =course.cid 
where num <60;

  1. 查询选修了 “生物课” 的所有学生ID、学生姓名、成绩。

    select * from score left join course on score.course_id =course.cid where course.cname="生物";


select 
    student.sid,
    student.sname,
    score.num 
from 
    score 
    left join course on score.course_id =course.cid 
    left join student on score.student_id=student.sid 
where course.cname="生物";

  2. 查询选修了 “生物课” 且分数低于60的的所有学生ID、学生姓名、成绩。

    select student.sid,student.sname,score.num from score left join course on score.course_id =course.cid left join student on score.student_id=student.sid where course.cname="生物" and score.num < 60;

  3. 查询所有同学的学号、姓名、选课数、总成绩。

    select student_id,count(1),sum(num) from score group by student_id;

select student_id,student.sname,count(1),sum(num) from score left join student on score.student_id=student.sid group by student_id;

  4. 查询各科被选修的学生数。

    select course_id,count(1) from score group by course_id;

select course_id,course.cname,count(1) from score left join course on score.course_id =course.cid group by course_id;

  5. 查询各科成绩的总分、最高分、最低分，显示：课程ID、课程名称、总分、最高分、最低分。

    select course_id,course.cname,sum(num), max(num), min(num) from score left join course on score.course_id =course.cid group by course_id;

  6. 查询各科成绩的平均分，显示：课程ID、课程名称、平均分。

    select course_id,course.cname,avg(num) from score left join course on score.course_id =course.cid group by course_id;

  7. 查询各科成绩的平均分，显示：课程ID、课程名称、平均分（按平均分从大到小排序）。

    select course_id,course.cname,avg(num) from score left join course on score.course_id =course.cid group by course_id order by avg(num) desc;


select course_id,course.cname,avg(num) as A from score left join course on score.course_id =course.cid group by course_id order by A desc;

  8. 查询各科成绩的平均分和及格率，显示：课程ID、课程名称、平均分、及格率。

    10/20 = 及格率

select course_id,count(1) from score group by course_id;

    select 
    sid,
    course_id,
    num,
    case when score.num >= 60 then 1 else 0 end "是否及格" 
from score;

    select sid,course_id,num,case when score.num > 60 then 1 else 0 end "是否及格" from score;

    select 
    course_id,
    course.cname,
    avg(num),
    count(1) as total,
    sum(case when score.num > 60 then 1 else 0 end) 
from 
    score 
    left join course on score.course_id =course.cid 
group by 
    course_id;

    select 
    course_id,
    course.cname,
    avg(num),
    sum(case when score.num > 60 then 1 else 0 end)/count(1) *100 as percent 
from 
    score 
    left join course on score.course_id =course.cid 
group by 
    course_id;

  9. 查询平均成绩大于60的所有学生的学号、平均成绩；

    select student_id,avg(num) from score group by student_id having avg(num) > 60;

  10. 查询平均成绩大于85的所有学生的学号、平均成绩、姓名。

    select student_id,avg(num) from score group by student_id having avg(num) > 85;

select student_id,avg(num),student.sname from score left join student on score.student_id=student.sid   group by student_id having avg(num) > 85;

  11. 查询 “三年二班” 每个学生的 学号、姓名、总成绩、平均成绩。

    SELECT
    * 
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid
    LEFT JOIN class ON class.cid = student.class_id;

    SELECT
    * 
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid
    LEFT JOIN class ON class.cid = student.class_id 
WHERE
    class.caption = "三年二班";

    SELECT
    student_id,
    sname,
    sum( num ),
    avg( num ) 
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid
    LEFT JOIN class ON class.cid = student.class_id 
WHERE
    class.caption = "三年二班" 
GROUP BY
    student_id

  12. 查询各个班级的班级名称、总成绩、平均成绩、及格率（按平均成绩从大到小排序）。

    SELECT
    class.cid,
    class.caption,
    sum( num ),
    avg( num ) as av,
    sum( CASE WHEN score.num > 60 THEN 1 ELSE 0 END ) / count( 1 ) * 100 as JG
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid
    LEFT JOIN class ON class.cid = student.class_id 
GROUP BY
    class.cid
ORDER BY
    av desc

  13. 查询学过 “波多” 老师课的同学的学号、姓名。

    SELECT
    student.sid,
    student.sname
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid
    LEFT JOIN course ON score.course_id = course.cid
    LEFT JOIN teacher ON course.teacher_id = teacher.tid
WHERE
    teacher.tname = "波多"

  14. 查询没学过 “波多” 老师课的同学的学号、姓名。

    SELECT
    student.sid,
    student.sname
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid
    LEFT JOIN course ON score.course_id = course.cid
    LEFT JOIN teacher ON course.teacher_id = teacher.tid
WHERE
    teacher.tname != "波多" 

    select * from student where sid not in(
    SELECT
        student.sid
    FROM
        score
        LEFT JOIN student ON score.student_id = student.sid
        LEFT JOIN course ON score.course_id = course.cid
        LEFT JOIN teacher ON course.teacher_id = teacher.tid
    WHERE
        teacher.tname = "波多" 
)

  15. 查询选修 “苍空” 老师所授课程的学生中，成绩最高的学生姓名及其成绩（不考虑并列）。

    SELECT
    student.sid,
    student.sname 
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid
    LEFT JOIN course ON score.course_id = course.cid
    LEFT JOIN teacher ON course.teacher_id = teacher.tid 
WHERE
    teacher.tname = "苍空" 
ORDER BY
    score.num DESC 
    LIMIT 1

  16. 查询选修 “苍空” 老师所授课程的学生中，成绩最高的学生姓名及其成绩（考虑并列）。

    SELECT
    student.sid,
    student.sname 
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid
    LEFT JOIN course ON score.course_id = course.cid
    LEFT JOIN teacher ON course.teacher_id = teacher.tid 
WHERE
    teacher.tname = "苍空" 
    AND score.num = (
        SELECT
            max( num ) 
        FROM
            score
            LEFT JOIN course ON score.course_id = course.cid
            LEFT JOIN teacher ON course.teacher_id = teacher.tid 
        WHERE
        teacher.tname = "苍空" 
    )

  17. 查询只选修了一门课程的全部学生的学号、姓名。

    SELECT
    student.sid,
    student.sname 
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid 
GROUP BY
    student_id 
HAVING
    count( 1 ) =1

  18. 查询至少选修两门课程的学生学号、学生姓名、选修课程数量。

    SELECT
    student.sid,
    student.sname ,
    count(1)
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid 
GROUP BY
    student_id 
HAVING
    count( 1 ) >= 2

  19. 查询两门及以上不及格的同学的学号、学生姓名、选修课程数量。

    SELECT
    student.sid,
    student.sname ,
    count(1)
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid 
where 
    num < 60
GROUP BY
    student_id 
HAVING
    count( 1 ) >= 2

  20. 查询选修了所有课程的学生的学号、姓名。

    SELECT
    student.sid,
    student.sname
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid 
GROUP BY
    student_id 
HAVING
    count( 1 ) = ( SELECT count( 1 ) FROM course )

  21. 查询未选修所有课程的学生的学号、姓名。

    SELECT
    student.sid,
    student.sname
FROM
    score
    LEFT JOIN student ON score.student_id = student.sid 
GROUP BY
    student_id 
HAVING
    count( 1 ) != ( SELECT count( 1 ) FROM course )

  22. 查询所有学生都选修了的课程的课程号、课程名。

    SELECT
    course.cid,
    course.cname
FROM
    score
    LEFT JOIN course ON score.course_id = course.cid
GROUP BY
    course_id 
HAVING
    count( 1 ) = ( SELECT count( 1 ) FROM student )

  23. 查询选修 “生物” 和 “物理” 课程的所有学生学号、姓名。

    SELECT
    student.sid,
    student.sname
FROM
    score
    LEFT JOIN course ON score.course_id = course.cid
    LEFT JOIN student ON score.student_id = student.sid
WHERE
    course.cname in ("生物","物理")
GROUP BY
    student_id
having 
    count(1) = 2;

  24. 查询至少有一门课与学号为“1”的学生所选的课程相同的其他学生学号 和 姓名 。

    SELECT
    student.sid,
    student.sname
FROM
    score
    LEFT JOIN course ON score.course_id = course.cid
    LEFT JOIN student ON score.student_id = student.sid
WHERE
    score.course_id in ( select course_id from score where student_id=1)
    and score.student_id != 1
GROUP BY
    student_id
HAVING
    count(1) >= 1

  25. 查询与学号为 “2” 的同学选修的课程完全相同的其他 学生学号 和 姓名 。

    SELECT
    student.sid,
    student.sname
FROM
    score
    LEFT JOIN course ON score.course_id = course.cid
    LEFT JOIN student ON score.student_id = student.sid
WHERE
    score.course_id in ( select course_id from score where student_id=2)
    and score.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=2)
    )
GROUP BY
    student_id
HAVING
    count(1) = ( select count(1) from score where student_id=2 )
-----------------------------------------------------------------
SELECT 
student.sid, student.sname 
FROM score 
LEFT JOIN student ON score.student_id = student.sid 
WHERE score.course_id in ( select course_id from score where student_id=2)  
and (select count(1) from score where student_id=student.sid) = (select count(1) from score where student_id=2) 
and student.sid !=2
GROUP BY student_id;


SELECT 
student.sid,case when (score.course_id not exists( select course_id from score where student_id=2)) student.sname else 1 end as student.sname
FROM score 
LEFT JOIN student ON score.student_id = student.sid 
WHERE (select count(1) from score where student_id=student.sid) = (select count(1) from score where student_id=2) 
and student.sid !=2
GROUP BY student_id;

-----------------------------------------------------------------

# 如果id=2学生他的课程数量和其他人的课程数量是一样。
select student_id from score where student_id!=2 group by student_id having count(1) = (select count(1) from score where student_id=2) -- 判断其他学生 报课数量 是否 和id2 相等

select 
    student_id 
from 
    score 
where 
    student_id!=2 
group by 
    student_id 
having 
    count(1) = select count(1) from score where student_id=2

  26. 查询“生物”课程比“物理”课程成绩高的所有学生的学号；

    SELECT
    * 
FROM
    score
    LEFT JOIN course ON score.course_id = course.cid
where 
    cname in ("生物","物理");

    SELECT
    *,
    case cname WHEN "生物" then num else -1 end sw,
    case cname WHEN "物理" then num else -1 end wl
FROM
    score
    LEFT JOIN course ON score.course_id = course.cid
where 
    cname in ("生物","物理");

    SELECT
    student_id,
    max(case cname WHEN "生物" then num else -1 end) as sw,
    max(case cname WHEN "物理" then num else -1 end) as wl
FROM
    score
    LEFT JOIN course ON score.course_id = course.cid
where 
    cname in ("生物","物理")
GROUP BY
    student_id;

    SELECT
    student_id,
    max( CASE cname WHEN "生物" THEN num ELSE 0 END ) AS sw,
    max( CASE cname WHEN "物理" THEN num ELSE 0 END ) AS wl 
FROM
    score
    LEFT JOIN course ON score.course_id = course.cid 
WHERE
    cname IN ( "生物", "物理" ) 
GROUP BY
    student_id 
HAVING
    sw > wl;

  27. 查询每门课程成绩最好的前3名 (不考虑成绩并列情况) 。

    SELECT cid,cname,
( select student.sname from score left join student on student.sid = score.student_id where course_id = course.cid order by num desc limit 1 offset 0) as "第1名",
( select student.sname from score left join student on student.sid = score.student_id where course_id = course.cid order by num desc limit 1 offset 1) as "第2名",
( select student.sname from score left join student on student.sid = score.student_id where course_id = course.cid order by num desc limit 1 offset 2) as "第3名"
FROM course;
-- where course_id = course.cid  值是从外层的查询中取得。

SELECT cid,cname, -- 添加分数列
( select student.sname from score left join student on student.sid = score.student_id where course_id = course.cid order by num desc limit 1 offset 0) as "第1名",
( select score.num from score left join student on student.sid = score.student_id where course_id = course.cid order by num desc limit 1 offset 0) as "num",
( select student.sname from score left join student on student.sid = score.student_id where course_id = course.cid order by num desc limit 1 offset 1) as "第2名",
( select score.num from score left join student on student.sid = score.student_id where course_id = course.cid order by num desc limit 1 offset 1) as "num",
( select student.sname from score left join student on student.sid = score.student_id where course_id = course.cid order by num desc limit 1 offset 2) as "第3名",
( select score.num from score left join student on student.sid = score.student_id where course_id = course.cid order by num desc limit 1 offset 2) as "num"
FROM course;

  28. 查询每门课程成绩最好的前3名 (考虑成绩并列情况) 。

    SELECT
    cid,
    cname,
    ( select num from score  where course_id = course.cid GROUP BY num order by num desc limit 1 offset 0) as "最高分",
    ( select num from score  where course_id = course.cid GROUP BY num order by num desc limit 1 offset 1) as "第二高分",
    ( select num from score  where course_id = course.cid GROUP BY num order by num desc limit 1 offset 2) as "第三高分"
FROM
    course;

    select * 
from score 
left join (
SELECT cid,cname,
( select num from score  where course_id = course.cid GROUP BY num order by num desc limit 1 offset 0) as "最高分",
( select num from score  where course_id = course.cid GROUP BY num order by num desc limit 1 offset 1) as "第二高分",
( select num from score  where course_id = course.cid GROUP BY num order by num desc limit 1 offset 2) as third
FROM course ) as C on score.course_id = C.cid 
WHERE score.num >= C.third;

  29. 创建一个表 sc，然后将 score 表中所有数据插入到 sc 表中。

    CREATE TABLE `sc` (
  `sid` int NOT NULL AUTO_INCREMENT PRIMARY KEY,
  `student_id` int NOT NULL,
  `course_id` int NOT NULL,
  `num` int NOT NULL,
  CONSTRAINT `fk_sc_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
  CONSTRAINT `fk_sc_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
) DEFAULT CHARSET=utf8;

    INSERT INTO sc SELECT * from score;

  30. 向 sc 表中插入一些记录，这些记录要求符合以下条件：

    • 学生ID为：没上过课程ID为 “2” 课程的学生的 学号；
    • 课程ID为：2
    • 成绩为：80
    -- 上过
select student_id from score where course_id =2;

-- 没上过
SELECT
    sid
FROM
    student 
WHERE
    sid NOT IN ( SELECT student_id FROM score WHERE course_id = 2 )


-- 构造数据
SELECT
    sid,
    2,
    80
FROM
    student 
WHERE
    sid NOT IN ( SELECT student_id FROM score WHERE course_id = 2 );

    INSERT INTO sc ( student_id, course_id, num ) SELECT
sid,
2,
80 
FROM
    student 
WHERE
    sid NOT IN ( SELECT student_id FROM score WHERE course_id = 2 )

  31. 向 sc 表中插入一些记录，这些记录要求符合以下条件：

    • 学生ID为：没上过课程ID为 “2” 课程的学生的 学号。
    • 课程ID为：2。
    • 成绩为：课程ID为3的最高分。
    SELECT
sid,
2,
(select max(num) from score where course_id=3) as num
FROM
    student 
WHERE
    sid NOT IN ( SELECT student_id FROM score WHERE course_id = 2 );

    INSERT INTO sc ( student_id, course_id, num ) SELECT
sid,
2,
(select max(num) from score where course_id=3) as num
FROM
    student 
WHERE
    sid NOT IN ( SELECT student_id FROM score WHERE course_id = 2 )

2. 设计表结构

根据如下的业务需求设计相应的表结构，内部需涵盖如下功能。

  • 注册
  • 登录
  • 发布博客
  • 查看博客列表，显示博客标题、创建时间、阅读数量、评论数量、赞数量等。
  • 博客详细，显示博文详细、评论 等。
  • 发表评论
  • 赞 or 踩
  • 阅读数量 + 1

参考如下图片请根据如下功能来设计相应的表结构。

注意：只需要设计表结构，不需要用python代码实现具体的功能（再学一点知识点后再更好的去实现）。

2.1 注册和登录

image-20210520204812764

2.2 文章列表

image-20210520204735867

2.3 文章详细

image-20210520205148509

2.4 评论 & 阅读 & 赞 & 踩

image-20210520205332907

注意：假设都是一级评论（不能回复评论）。

博客系统 - 表结构设计

image-20210531083345193

drop database blog;
drop database IF EXISTS blog;
create database blog default charset utf8 collate utf8_general_ci;
use blog;

create table user(
    id int not null auto_increment primary key,
    username varchar(16) not null,
    nickname varchar(16) not null,
    mobile char(11) not null,
    password varchar(64) not null,
    email varchar(64) not null,
    ctime datetime not null
)default charset=utf8;


create table article(
    id int not null auto_increment primary key,
    title varchar(255) not null,
    text text not null,
    read_count int default 0,
    comment_count int default 0,
    up_count int default 0,
    down_count int default 0,
    user_id int not null,
    ctime datetime not null,
    constraint fk_article_user foreign key (user_id) references user(id)
)default charset=utf8;


create table comment(
    id int not null auto_increment primary key,
    content varchar(255) not null,
    user_id int not null,
    article_id int not null,
    ctime datetime not null,
    constraint fk_comment_user foreign key (user_id) references user(id),
    constraint fk_comment_article foreign key (article_id) references article(id)
)default charset=utf8;


create table up_down(
    id int not null auto_increment primary key,
    choice tinyint not null,
    user_id int not null,
    article_id int not null,
    ctime datetime not null,
    constraint fk_up_down_user foreign key (user_id) references user(id),
    constraint fk_up_down_article foreign key (article_id) references article(id)
)default charset=utf8;