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@@ -0,0 +1,147 @@
+# 笔记
+
+```sql
+分组函数
+
+类型 sum avg min max count
+
+特点
+sum,avg一般用于处理数据类型
+max,min,count可以处理任何类型
+sum,avg,max,min,count都忽略null值
+
+可以与distinct搭配使用
+
+    SELECT SUM(DISTINCT salary)，SUM(salary) FROM employees;
+
+```
+
+```
+关联查询
+内连接 select e.ename, d.dname from emp e join dept d on(e.deptno = d.deptno);
+外连接
+* left 左外连接
+* right 右外连接
+* full 全外连接
+*     select * from 表名一 left|right|full [outer] join 表名二 on 表名一.column1 = 表名二.column2;
+
+```
+
+# 作业
+
+```sql
+create database zuoye charset utf8;
+use zuoye;
+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
+);
+
+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/
+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 
+
+4.查询
+①　查询Score表中的最高分的学生学号和课程号。
+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。
+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。
+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。
+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。
+select avg(score.Degree) from score inner join student on student.Sno = score.Sno where student.Class = '95033';
+
+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。
+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。
+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。
+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。
+⑩　查询“张旭“教师任课的学生成绩。
+⑪　查询选修某课程的同学人数多于5人的教师姓名。
+⑫　查询出“计算机系“教师所教课程的成绩表。
+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。
+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。
+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.
+⑯　查询成绩比该课程平均成绩低的同学的成绩表。
+⑰　查询所有任课教师的Tname和Depart.
+⑱　查询所有未讲课的教师的Tname和Depart.
+⑲　查询“男”教师及其所上的课程。
+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。
+21　查询和“李军”同性别的所有同学的Sname.
+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.
+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。
+
+
+```
+
+
+
+