练习题

s4day60

上节回顾：
    1. MySQL：文件管理的软件
    2. 三部分：
        - 服务端
        - SQL语句
        - 客户端
    3. 客户端：
        - mysql
        - navicat
        
    4. 授权操作
        - 用户操作
        - 授权操作
    5. SQL语句
        - 数据库操作
            - create database xx default charset utf8;
            - drop database xx;
        - 数据表
            - 列
                - 数字
                    整数
                    小数
                - 字符串
                - 时间
                - 二进制
            - 其他：引擎，字符编码，起始值
            
            - 主键索引
            - 唯一索引
            - 外键
                - 一对多
                - 一对一
                - 多对多
        - 数据行
            - 增
            - 删
            - 改
            - 查
                - in   not in 
                - between and
                - limit
                - group by  having
                - order by 
                - like "%a"
                - left join xx on  关系
                - 临时表
                    select * from (select * from tb where id< 10) as B;
                    
                - 
                    select 
                        id,
                        name,
                        1,
                        (select count(1) from tb)
                    from tb2
                    
                    SELECT 
                        student_id,
                        (select num from score as s2 where s2.student_id=s1.student_id and course_id = 1) as 语文,
                        (select num from score as s2 where s2.student_id=s1.student_id and course_id = 2) as 数学,
                        (select num from score as s2 where s2.student_id=s1.student_id and course_id = 3) as 英语
                    from score as s1;

                - 条件
                    select 
                        course_id,
                        max(num),
                        min(num),
                        min(num)+1,
                        case when min(num) <10 THEN 0 ELSE min(num) END as c  
                    from score GROUP BY course_id
                    
                    select course_id,avg(num),sum(case when num <60 THEN 0 ELSE 1 END),sum(1),sum(case when num <60 THEN 0 ELSE 1 END)/sum(1) as jgl from score GROUP BY course_id order by AVG(num) asc,jgl desc;
        PS: 数据放在硬盘上
    
    
    
    思想：
        - 操作
        - 设计
    

    
今日内容：
    1. 练习题
        7、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；
        -- select score.student_id,student.sname from score
        -- 
        -- left join student on score.student_id=student.sid
        -- 
        -- where course_id =1 or course_id =2 GROUP BY student_id HAVING count(course_id) > 1


        8、查询学过“叶平”老师所教的所有课的同学的学号、姓名；
        -- select student_id from score where course_id in (
        --     select cid from course left JOIN teacher on course.teacher_id = teacher.tid where teacher.tname = "李平老师"
        -- ) GROUP BY student_id having count(course_id) =  (select count(cid) from course left JOIN teacher on course.teacher_id = teacher.tid where teacher.tname = "李平老师")
        -- 
        --
        10、查询有课程成绩小于60分的同学的学号、姓名；
        -- select student_id from score where num < 60 GROUP BY student_id
        -- select DISTINCT student_id from score where num < 60

        -- 查询没有学全所有课的同学的学号、姓名；

        11、查询没有学全所有课的同学的学号、姓名；
        -- select student_id,count(1) from score GROUP BY student_id  HAVING count(1) < (select count(cid) from course);
        -- 

        -- 12、查询至少有一门课与学号为“001”的同学所学相同的同学的学号和姓名；
        -- select course_id from score where student_id = 1;
        -- select student_id from score where student_id != 1 and course_id in (select course_id from score where student_id = 1) GROUP BY student_id

        -- 13、查询至少学过学号为“001”同学所有课的其他同学学号和姓名；
        -- select course_id from score where student_id = 1;
        -- select student_id,count(1) from score where student_id != 1 and course_id in (select course_id from score where student_id = 1) GROUP BY student_id HAVING count(1) = (select count(course_id) from score where student_id = 1)


        -- 14、查询和“002”号的同学学习的课程完全相同的其他同学学号和姓名；

        -- 获取和方少伟选课个数相同的通许
        -- select count(1) from score where student_id = 1;
        -- 

        -- select student_id from score where  student_id in (
        --     select student_id from score where student_id !=1 GROUP BY student_id HAVING count(1) = (select count(1) from score where student_id = 1)
        -- ) and course_id in (select course_id from score where student_id = 1) GROUP BY student_id HAVING count(1) = (select count(1) from score where student_id = 1)
        -- 
        -- 
        -- insert into tb(student_id,course_id,num) 
        -- 
        -- select student_id,2,(SELECT AVG(num) from score where course_id = 2) from score where course_id != 2

        -- 17、按平均成绩从低到高 显示所有学生的“语文”、“数学”、“英语”三门的课程成绩，按如下形式显示： 学生ID,语文,数学,英语,有效课程数,有效平均分；
        -- 1  90  80   99
        -- 2  90  80   99
        -- SELECT 
        --     student_id,
        --     (select num from score as s2 where s2.student_id=s1.student_id and course_id = 1) as 语文,
        --     (select num from score as s2 where s2.student_id=s1.student_id and course_id = 2) as 数学,
        --     (select num from score as s2 where s2.student_id=s1.student_id and course_id = 3) as 英语
        -- from score as s1;
        -- 
        -- 18、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分；
        -- select course_id,max(num),min(num),min(num)+1,case when min(num) <10 THEN 0 ELSE min(num) END as c  from score GROUP BY course_id

        -- 19、按各科平均成绩从低到高和及格率的百分数从高到低顺序；


        select course_id,avg(num),sum(case when num <60 THEN 0 ELSE 1 END),sum(1),sum(case when num <60 THEN 0 ELSE 1 END)/sum(1) as jgl from score GROUP BY course_id order by AVG(num) asc,jgl desc;


    
    

    pymysql模块：
        pip3 install pymysql -i https://pypi.douban.com/simple
        Python模块：对数据库进行操作（SQL语句）
        
        1. Python实现用户登录
        2. MySQL保存数据
        
        
        - 连接、关闭（游标）
        - execute()   -- SQL注入
        - 增删改： conn.commit()
        - fetchone fetchall
        - 获取插入数据自增ID
        
        
练习：

    权限管理
    
        权限表：
            1   订单管理
            2   用户管理
            3   菜单管理
            4   权限分配
            5   Bug管理
        
        用户表：
            1   Alex
            2   egon
        
        用户权限关系表：
            1    1
            1    2
            2    1
            
    Python实现：

        某个用户登录后，查看自己拥有所有权限