问题2就不会了。。。

SELECT * FROM mysql.user WHERE user='root'\G;

  CREATE TABLE IF NOT EXISTS class(
    c_id TINYINT UNSIGNED  NOT NULL AUTO_INCREMENT KEY COMMENT '编号',
    name VARCHAR(50) NOT NULL UNIQUE COMMENT '班级',
    descrip VARCHAR(50)  NOT NULL COMMENT '备注'
  );

  CREATE TABLE IF NOT EXISTS student(
    s_id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT KEY COMMENT '编号',
    name VARCHAR(50) NOT NULL COMMENT '姓名',
    gender ENUM('男','女') NOT NULL DEFAULT '男' COMMENT '性别',
    class TINYINT NOT NULL COMMENT '班级'
  );

  CREATE TABLE IF NOT EXISTS score(
    sc_id TINYINT UNSIGNED NOT NULL AUTO_INCREMENT KEY COMMENT '编号',
    s_id SMALLINT UNSIGNED NOT NULL COMMENT '学生ID',
    course VARCHAR(50) NOT NULL COMMENT '课程',
    mark TINYINT UNSIGNED NOT NULL COMMENT'分数'
  );

  --2、查询每个班级中每一科的平均成绩，显示数据包括班级名称，课程以及平均分数，并按照班ID升序排列
  SELECT c.name,s.course,AVG(s.mark)
  FROM score AS s
  JOIN class AS c
  JOIN student AS t
  on c.c_id=t.s_id and t.s_id=s.s_id
  GROUP BY c.c_id,c.name,s.course
  ;

  INSERT class(c_id,name,descrip) VALUES(001,'一年级一班','重点班'),
  (002,'一年级二班','重点班'),
  (003,'二年级一班','重点班'),
  (004,'二年级二班','普通班');

INSERT student(s_id,name,gender,class) VALUES(1001,'赵晓明','男',001),
(1002,'王晓红','女',001),
(1003,'张晓晓','女',001),
(1004,'孙琪琪','女',003),
(1005,'李米米','女',004),
(1006,'赵晓刚','男',003),
(1007,'张大宝','男',002),
(1008,'张兰','女',004),
(1009,'孙好','男',001);

INSERT score(sc_id,s_id,course,mark) VALUES(001,1001,'数学',98),
(002,1001,'语文',90),
(003,1001,'英语',97),
(004,1002,'数学',96),
(005,1002,'语文',88),
(006,1003,'语文',88),
(007,1002,'英文',91),
(008,1003,'数学',96),
(009,1003,'英语',86),
(010,1004,'英语',89),
(011,1004,'英语',82),
(012,1004,'英语',83),
(013,1005,'英语',75),
(014,1005,'英语',86),
(015,1005,'英语',77),
(016,1006,'英语',81),
(017,1006,'英语',77),
(018,1006,'英语',60),
(019,1007,'英语',89),
(020,1007,'英语',56),
(021,1007,'英语',70),
(022,1008,'英语',87),
(023,1008,'英语',55),
(024,1008,'英语',66),
(025,1009,'英语',78),
(026,1009,'英语',60),
(027,1009,'英语',52);

源码贴上 求救