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+```mysql
+create database zuoye2 charset utf8;
+use zuoye2;
+
+create table student(
+ sno varchar(20)primary key,
+ sname varchar(20)not null,
+ ssex varchar(20)not null,
+ sbirthday datetime,
+ class varchar(20)
+);
+
+create table course(
+	cno varchar(20)primary key,
+	cname varchar(20) not null,
+	tno varchar(20)not null,
+	foreign key (tno) references teacher(tno)
+);
+
+create table score(
+	sno varchar(20)not null,
+	cno varchar(20)not null,
+	degree decimal(4,1),
+	foreign key (sno) references student(sno),
+	foreign key (cno) references course(cno)
+);
+
+create table teacher(
+	tno varchar(20)primary key,
+	tname varchar(20)not null,
+	tsex varchar(20)not null,
+	tbirthday datetime,
+	prof varchar(20),
+	depart varchar(20)not null
+);
+
+insert into student values(108,'曾华','男','1977-9-1','95033');
+insert into student values(105,'匡明','男','1975-10-2','95031');
+insert into student values(107,'王丽','女','1976-1-23','95033');
+insert into student values(101,'李军','男','1976-2-20','95033');
+insert into student values(109,'王芳','女','1975-2-10','95031');
+insert into student values(103,'陆君','男','1974-6-3','95031');
+
+insert into course values('3-105','计算机导论','825');
+insert into course values('3-245','操作系统','804');
+insert into course values('6-166','数字电路','856');
+insert into course values('9-888','高等数学','831');
+
+insert into score values('103','3-245','86');
+insert into score values('105','3-245','75');
+insert into score values('109','3-245','68');
+insert into score values('103','3-105','92');
+insert into score values('105','3-105','88');
+insert into score values('109','3-105','76');
+insert into score values('101','3-105','64');
+insert into score values('107','3-105','91');
+insert into score values('108','3-105','78');
+insert into score values('101','6-166','85');
+insert into score values('107','6-166','79');
+insert into score values('108','6-166','81');
+
+insert into teacher values('804','李诚','男','1958-12-2','副教授','计算机系');
+insert into teacher values('856','张旭','男','1969-3-12','讲师','电子工程系');
+insert into teacher values('825','王萍','女','1972-5-5','助教','计算机系');
+insert into teacher values('831','刘冰','女','1977-8-14','助教','电子工程系');
+
+
+```
+
+-- 1,查询所有学生，都学了哪些课程，要显示学生信息和课程信息/
+
+```mysql
+select student.sno,sname,ssex,sbirthday,class,cname 
+from student left join score on student.sno=score.sno 
+left join course on score.cno=course.cno;
+```
+
+-- 2，查询没有学生的教师的所有信息\
+
+```mysql
+select * from teacher;
+select * from score;
+
+select * from course;
+```
+
+-- 4.查询
+-- ①　查询Score表中的最高分的学生学号和课程号。
+
+```mysql
+select sno,cno from score where degree=(select max(degree) from score);
+```
+
+-- ②　查询所有学生的Sname、Cno和Degree列。
+
+```mysql
+select sname,score.cno,degree from student inner join score on student.sno=score.sno;
+```
+
+-- ③　查询所有学生的Sno、Cname和Degree列。
+
+```mysql
+select score.sno,cname,degree from score inner join course on score.cno=course.cno;
+```
+
+-- ④　查询所有学生的Sname、Cname和Degree列。
+
+```mysql
+select sname,cname,degree from student inner join score on student.sno=score.sno inner join course on score.cno=course.cno;
+```
+
+-- ⑤　查询“95033”班学生的平均分。
+
+```mysql
+
+```
+
+-- ⑥　查询选修“3-105”课程的成绩高于“109”号同学成绩的所有同学的记录。
+
+```mysql
+select * from student 
+inner join score on student.sno=score.sno 
+where score.cno='3-105' and degree > 
+(select degree from score where score.sno=109 and score.cno='3-105' );
+```
+
+-- ⑦　查询score中选学多门课程的同学中分数为非最高分成绩的记录。
+
+```mysql
+
+```
+
+-- ⑧　查询成绩高于学号为“109”、课程号为“3-105”的成绩的所有记录。
+
+```mysql
+select * from score 
+where degree>(
+select degree from score where score.sno=109 and score.cno='3-105');
+```
+
+-- ⑨　查询和学号为108的同学同年出生的所有学生的Sno、Sname和Sbirthday列。
+
+```mysql
+select sno,sname,sbirthday from 
+student where sbirthday=(select sbirthday from student where sno=108);
+```
+
+-- 这个只有他自己生日一样下面是不输出他自己生日的代码
+
+```mysql
+select sno,sname,sbirthday from student 
+where sbirthday=(select sbirthday from student where sno=108)
+and sno!=108;
+```
+
+-- ⑩　查询“张旭“教师任课的学生成绩。
+
+```mysql
+
+```
+
+-- ⑪　查询选修某课程的同学人数多于5人的教师姓名。
+
+```mysql
+
+```
+
+-- ⑫　查询出“计算机系“教师所教课程的成绩表。
+
+```mysql
+select score.sno,score.cno,degree from score left join course 
+on score.cno=course.cno 
+left join teacher
+on course.tno=teacher.tno
+where depart='计算机系';
+```
+
+-- ⑬　查询“计算机系”与“电子工程系“不同职称的教师的Tname和Prof。
+
+```mysql
+select tname,prof from teacher where prof in (select distinct prof from teacher);
+```
+
+-- ⑭　查询选修编号为“3-105“课程且成绩至少高于选修编号为“3-245”的同学的Cno、Sno和Degree,并按Degree从高到低次序排序。
+
+```mysql
+
+```
+
+-- ⑮　查询选修编号为“3-105”且成绩高于选修编号为“3-245”课程的同学的Cno、Sno和Degree.
+
+```mysql
+select score.cno,score.sno,score.degree from 
+score inner join course 
+on score.cno = course.cno 
+and score.cno = '3-105' 
+and score.degree >  (
+select max(degree) from score where score.cno='3-245');
+```
+
+-- ⑯　查询成绩比该课程平均成绩低的同学的成绩表。
+
+```mysql
+select 
+
+
+```
+
+-- ⑰　查询所有任课教师的Tname和Depart.
+
+```mysql
+
+```
+
+-- ⑱　查询所有未讲课的教师的Tname和Depart.
+
+```mysql
+
+```
+
+-- ⑲　查询“男”教师及其所上的课程。
+
+```mysql
+select tname,cname from teacher left join course
+on teacher.tno=course.tno
+where tsex='男';
+```
+
+-- ⑳　查询最高分同学的Sno、Cno和Degree列。
+
+```mysql
+select sno,cno,degree from score where degree=(
+select max(degree) from score);
+```
+
+-- 21　查询和“李军”同性别的所有同学的Sname.
+
+```mysql
+select sname from student 
+where ssex=(select ssex from student where sname='李军')；
+```
+
+-- 22　查询和“李军”同性别并同班的同学Sname.
+
+```mysql
+select sname from student 
+where ssex=(select ssex from student where sname='李军')
+and class=(select class from student where sname='李军');
+```
+
+-- 23　查询所有选修“计算机导论”课程的“男”同学的成绩表。
+
+```mysql
+select score.* from score left join course
+on score.cno=course.cno 
+left join student
+on score.sno=student.sno
+where score.cno=(select course.cno from course where cname='计算机导论')
+and ssex='男';
+```
+