From 4780324f3be44e1e8582e00a9d64a894d6416634 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9E=97=E6=99=9F=E8=BE=89?= <2081404735@qq.com>
Date: Wed, 1 Mar 2023 12:31:53 +0800
Subject: [PATCH 1/2] =?UTF-8?q?=E8=81=94=E5=90=88=E6=9F=A5=E8=AF=A2?=
 =?UTF-8?q?=E7=AC=94=E8=AE=B0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 ...45\350\257\242\347\254\224\350\256\260.md" | 266 ++++++++++++++++++
 1 file changed, 266 insertions(+)
 create mode 100644 "06 \346\236\227\346\231\237\350\276\211/20230227 \350\201\224\345\220\210\346\237\245\350\257\242\347\254\224\350\256\260.md"

diff --git "a/06 \346\236\227\346\231\237\350\276\211/20230227 \350\201\224\345\220\210\346\237\245\350\257\242\347\254\224\350\256\260.md" "b/06 \346\236\227\346\231\237\350\276\211/20230227 \350\201\224\345\220\210\346\237\245\350\257\242\347\254\224\350\256\260.md"
new file mode 100644
index 0000000..195f3ec
--- /dev/null
+++ "b/06 \346\236\227\346\231\237\350\276\211/20230227 \350\201\224\345\220\210\346\237\245\350\257\242\347\254\224\350\256\260.md"	
@@ -0,0 +1,266 @@
+# 一、笔记
+
+```sql
+-- 1.内连接 A表和B表共有的
+SELECT 字段列表 FROM A表 INNER JOIN B表;
+-- 2.左连接 A表全部
+SELECT 字段列表 FROM A表 LEFT JOIN B表;
+-- 3.右连接 B表全部
+SELECT 字段列表 FROM A表 RIGHT JOIN B表;
+-- 4全外连接 A表全部和B表全部
+SELECT 字段列表 FROM A表 LEFT JOIN B表 
+ON A表.两表都有的列 = B表.两表都有的列
+UNION 
+SELECT 字段列表 FROM A表 RIGHT JOIN B表 
+ON A表.两表都有的列 = B表.两表都有的列；
+-- 5全外连接 除去A表和B表共有的
+SELECT 字段列表 FROM A表 LEFT JOIN B表 
+ON A表.两表都有的列 = B表.两表都有的列
+WHERE 条件
+UNION 
+SELECT 字段列表 FROM A表 RIGHT JOIN B表 
+ON A表.两表都有的列 = B表.两表都有的列
+WHERE 条件；
+```
+
+
+
+# 二、作业
+
+1. 设有一数据库,包括四个表：学生表（Student）、课程表（Course）、成绩表（Score）以及教师信息表（Teacher）。四个表的结构分别如表1-1的表（一）~表（四）所示,数据如表1-2的表（一）~表（四）所示。用SQL语句创建四个表并完成相关题目。
+-- 
+
+```sql
+create database yyg charset utf8;
+```
+
+2. **数据库的表结构**
+
+```sql
+use yyg;
+```
+
+
+表（一）Student (学生表)
+-- 
+| 属性名    | 数据类型     | 可否为空 | 含义         |
+| --------- | ------------ | -------- | ------------ |
+| Sno       | varchar (20) | 否       | 学号（主码） |
+| Sname     | varchar (20) | 否       | 学生姓名     |
+| Ssex      | varchar (20) | 否       | 学生性别     |
+| Sbirthday | datetime     | 可       | 学生出生年月 |
+| Class     | varchar (20) | 可       | 学生所在班级 |
+```sql
+create table Student(
+    Sno varchar(20) primary key comment"学号",
+    Sname varchar(20) not null comment"学生姓名",
+    Ssex varchar(20) not null comment"学生性别",
+    Sbirthday datetime comment'学生出生年月',
+    Class varchar(20) comment'学生所在班级'
+);
+```
+表（二）Course（课程表）
+-- 
+| 属性名 | 数据类型     | 可否为空 | 含义             |
+| ------ | ------------ | -------- | ---------------- |
+| Cno    | varchar (20) | 否       | 课程号（主码）   |
+| Cname  | varchar (20) | 否       | 课程名称         |
+| Tno    | varchar (20) | 否       | 教工编号（外码） |
+|        |              |          |                  |
+```sql
+create table Course(
+    Cno varchar (20) primary key comment'课程号',
+    Cname varchar(20) not null comment'课程名称 ',
+    Tno varchar(20)  not null comment'教工编号',
+    foreign key (Tno) references Teacher(Tno)
+);
+```
+表（三）Score(成绩表)
+-- 
+| 属性名         | 数据类型     | 可否为空 | 含义           |
+| -------------- | ------------ | -------- | -------------- |
+| Sno            | varchar (20) | 否       | 学号（外码）   |
+| Cno            | varchar (20) | 否       | 课程号（外码） |
+| Degree         | Decimal(4,1) | 可       | 成绩           |
+| 主码：Sno+ Cno |              |          |                |
+```sql
+create table Score(
+   Sno varchar(20) not null comment'学号',
+    Cno varchar(20) not null comment'课程号',
+    Degree Decimal(4,1) comment'成绩',
+    foreign key (Sno) references Student(Sno),
+    foreign key (Cno) references Course(Cno),
+    primary key(Sno,Cno)
+);
+```
+表（四）Teacher(教师表)
+-- 
+| 属性名    | 数据类型     | 可否为空 | 含义             |
+| --------- | ------------ | -------- | ---------------- |
+| Tno       | varchar (20) | 否       | 教工编号（主码） |
+| Tname     | varchar (20) | 否       | 教工姓名         |
+| Tsex      | varchar (20) | 否       | 教工性别         |
+| Tbirthday | datetime     | 可       | 教工出生年月     |
+| Prof      | varchar (20) | 可       | 职称             |
+| Depart    | varchar (20) | 否       | 教工所在部门     |
+```sql
+create table Teacher(
+    Tno varchar(20) primary key not null comment'教工编号',
+    Tname varchar(20)not null comment'教工姓名',
+    Tsex varchar(20)not null comment'教工性别',
+    Tbirthday datetime comment'教工出生年月',
+    Prof varchar(20) comment'职称',
+    Depart varchar(20)not null comment'教工所在部门'
+);
+```
+表（一）Student
+-- 
+| Sno  | Sname | Ssex | Sbirthday | class |
+| ---- | ----- | ---- | --------- | ----- |
+| 108  | 曾华  | 男   | 1977-9-1  | 95033 |
+| 105  | 匡明  | 男   | 1975-10-2 | 95031 |
+| 107  | 王丽  | 女   | 1976-1-23 | 95033 |
+| 101  | 李军  | 男   | 1976-2-20 | 95033 |
+| 109  | 王芳  | 女   | 1975-2-10 | 95031 |
+| 103  | 陆君  | 男   | 1974-6-3  | 95031 |
+```sql
+insert into Student values
+    ('108','曾华','男','1977-9-1','95033'),
+    ('105','匡明','男','1975-10-2','95031'),
+    ('107','王丽','女','1976-1-23','95033'),
+    ('101','李军','男','1976-2-20','95033'),
+    ('109','王芳','女','1975-2-10','95031'),
+    ('103','陆君','男','1974-6-3','95031');
+```
+ 表（二）Course
+-- 
+| Cno   | Cname      | Tno  |
+| ----- | ---------- | ---- |
+| 3-105 | 计算机导论 | 825  |
+| 3-245 | 操作系统   | 804  |
+| 6-166 | 数字电路   | 856  |
+| 9-888 | 高等数学   | 831  |
+```sql
+insert into Course values
+    ('3-105','计算机导论','825'),
+    ('3-245','操作系统','804'),
+    ('6-166','数字电路','856'),
+    ('9-888','高等数学','831');
+```
+
+表（三）Score
+-- 
+| Sno  | Cno   | Degree |
+| ---- | ----- | ------ |
+| 103  | 3-245 | 86     |
+| 105  | 3-245 | 75     |
+| 109  | 3-245 | 68     |
+| 103  | 3-105 | 92     |
+| 105  | 3-105 | 88     |
+| 109  | 3-105 | 76     |
+| 101  | 3-105 | 64     |
+| 107  | 3-105 | 91     |
+```sql
+insert into Score values
+    ('103','3-245','86'),
+    ('105','3-245','75'),
+    ('109','3-245','68'),
+    ('103','3-105','92'),
+    ('105','3-105','88'),
+    ('109','3-105','76'),
+    ('101','3-105','64'),
+    ('107','3-105','91'),
+    ('108','3-105','78'),
+    ('101','6-166','85'),
+    ('107','6-166','79'),
+    ('108','6-166','81');
+```
+表（四）Teacher
+-- 
+| Tno  | Tname | Tsex | Tbirthday | Prof   |
+| ---- | ----- | ---- | --------- | ------ |
+| 804  | 李诚  | 男   | 1958-12-2 | 副教授 |
+| 856  | 张旭  | 男   | 1969-3-12 | 讲师   |
+| 825  | 王萍  | 女   | 1972-5-5  | 助教   |
+| 831  | 刘冰  | 女   | 1977-8-14 | 助教   |
+```sql
+insert into Teacher values
+    (804,'李诚','男','1958-12-2','副教授','计算机系'),
+    (856,'张旭','男','1969-3-12','讲师','电子工程系'),
+    (825,'王萍','女','1972-5-5','助教','计算机系'),
+    (831,'刘冰','女','1977-8-14','助教','电子工程系');
+```
+3. **数据库中的数据**:
+-- 
+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/
+
+```sql
+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
+
+```sql
+select Teacher.Tno,Tname,Tsex,Tbirthday,Prof,Depart 
+from Teacher left join Course on Teacher.Tno = Course.Tno 
+left join Score on Course.Cno = Score.Cno 
+where Score.Sno is null;
+```
+
+
+4. 查询
+-- 
+```sql
+-- 1　查询Score表中的最高分的学生学号和课程号。
+select Sno 学号,Cno 课程号 from Score
+where Degree = (select max(Degree) from Score);
+-- 2　查询所有学生的Sname、Cno和Degree列。
+select Sname,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 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,Course,Score where Student.Sno=Score.Sno and Course.Cno=Score.Cno;
+-- 5　查询“95033”班学生的平均分。
+select avg(Degree) from Score inner join Student on Score.Sno=Student.Sno where 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。
+select * from Score where Degree>(select Degree from Score where Sno = '109' and Cno = '3-105' ) and 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。
+select * from Score a where Degree <(select MAX(degree) from Score b where a.Cno=b.Cno) and Sno in(select Sno from Score group by Sno having count(*)>1);
+-- 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。
+select * from Score where Degree >(select Degree from Score where Sno='109' and 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。
+select Sno,Sname,Sbirthday from Student where Sbirthday=(select Sbirthday from Student where Sno='108');
+-- 10　查询“张旭“教师任课的学生成绩。
+-select Sno,Degree from Score where Cno=(select Cno from Course inner join Teacher ON Course.Tno= Teacher.Tno where Tname='张旭' );
+-- 11　查询选修某课程的同学人数多于5人的教师姓名。
+select Tname from Teacher where Tno=(select Tno from Course where Cno=(select Cno from Score group by Cno having COUNT(Cno)>5));
+-- 12　查询出“计算机系“教师所教课程的成绩表。
+select sno,Cno ,Degree from Score where Cno in
+(select Cno from Course where Tno IN (select Tno from Teacher 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 from Teacher where Tno=(select Tno from Course where Cno=(select Cno from Score group by Cno having COUNT(Cno)>5));
+-- 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。
+select Cno,Sno,Degree from Score where Cno='3-105' and Degree>(select max(Degree) from Score where Cno= '3-245');
+-- 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.
+select Cno,Sno,Degree from Score where Cno='3-105' and Degree>(select max(Degree) from Score where Cno= '3-245');
+-- 16　查询成绩比该课程平均成绩低的同学的成绩表。
+select Cno,Sno,Degree from Score where Degree > avg(sum(select Degree from Score where Cno='3-245'));
+-- 17　查询所有任课教师的Tname和Depart.
+select Tname,Depart from Teacher;
+-- 18　查询所有未讲课的教师的Tname和Depart.
+select Tname,Depart from Teacher left join Course on Teacher.Tno=Course.Tno left join Score on Course.Cno=Score.Cno where Score.Cno is null;
+-- 19　查询“男”教师及其所上的课程。
+select Tname,Depart from Teacher where Tsex = '男';
+-- 20　查询最高分同学的Sno、Cno和Degree列。
+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.
+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。
+Select * from Score where Sno in (select Sno from Student where Ssex ='男')
+and Cno = (select Cno from Course where Cname='计算机导论');
+```
\ No newline at end of file
-- 
Gitee


From e9faa3ca29fc42292420401e26442c03ee1ba134 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9E=97=E6=99=9F=E8=BE=89?= <2081404735@qq.com>
Date: Wed, 1 Mar 2023 21:52:59 +0800
Subject: [PATCH 2/2] =?UTF-8?q?=E5=AD=90=E6=9F=A5=E8=AF=A2=E7=AC=94?=
 =?UTF-8?q?=E8=AE=B0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 ...45\350\257\242\347\254\224\350\256\260.md" | 265 ++++++++++++++----
 ...45\350\257\242\347\254\224\350\256\260.md" |  25 ++
 2 files changed, 235 insertions(+), 55 deletions(-)
 create mode 100644 "06 \346\236\227\346\231\237\350\276\211/20230301\345\255\220\346\237\245\350\257\242\347\254\224\350\256\260.md"

diff --git "a/06 \346\236\227\346\231\237\350\276\211/20230227 \350\201\224\345\220\210\346\237\245\350\257\242\347\254\224\350\256\260.md" "b/06 \346\236\227\346\231\237\350\276\211/20230227 \350\201\224\345\220\210\346\237\245\350\257\242\347\254\224\350\256\260.md"
index 195f3ec..cec8393 100644
--- "a/06 \346\236\227\346\231\237\350\276\211/20230227 \350\201\224\345\220\210\346\237\245\350\257\242\347\254\224\350\256\260.md"	
+++ "b/06 \346\236\227\346\231\237\350\276\211/20230227 \350\201\224\345\220\210\346\237\245\350\257\242\347\254\224\350\256\260.md"	
@@ -40,9 +40,8 @@ create database yyg charset utf8;
 use yyg;
 ```
 
-
 表（一）Student (学生表)
--- 
+
 | 属性名    | 数据类型     | 可否为空 | 含义         |
 | --------- | ------------ | -------- | ------------ |
 | Sno       | varchar (20) | 否       | 学号（主码） |
@@ -60,7 +59,7 @@ create table Student(
 );
 ```
 表（二）Course（课程表）
--- 
+
 | 属性名 | 数据类型     | 可否为空 | 含义             |
 | ------ | ------------ | -------- | ---------------- |
 | Cno    | varchar (20) | 否       | 课程号（主码）   |
@@ -76,7 +75,7 @@ create table Course(
 );
 ```
 表（三）Score(成绩表)
--- 
+
 | 属性名         | 数据类型     | 可否为空 | 含义           |
 | -------------- | ------------ | -------- | -------------- |
 | Sno            | varchar (20) | 否       | 学号（外码）   |
@@ -94,7 +93,7 @@ create table Score(
 );
 ```
 表（四）Teacher(教师表)
--- 
+
 | 属性名    | 数据类型     | 可否为空 | 含义             |
 | --------- | ------------ | -------- | ---------------- |
 | Tno       | varchar (20) | 否       | 教工编号（主码） |
@@ -114,7 +113,7 @@ create table Teacher(
 );
 ```
 表（一）Student
--- 
+
 | Sno  | Sname | Ssex | Sbirthday | class |
 | ---- | ----- | ---- | --------- | ----- |
 | 108  | 曾华  | 男   | 1977-9-1  | 95033 |
@@ -133,7 +132,7 @@ insert into Student values
     ('103','陆君','男','1974-6-3','95031');
 ```
  表（二）Course
--- 
+
 | Cno   | Cname      | Tno  |
 | ----- | ---------- | ---- |
 | 3-105 | 计算机导论 | 825  |
@@ -149,7 +148,7 @@ insert into Course values
 ```
 
 表（三）Score
--- 
+
 | Sno  | Cno   | Degree |
 | ---- | ----- | ------ |
 | 103  | 3-245 | 86     |
@@ -176,7 +175,7 @@ insert into Score values
     ('108','6-166','81');
 ```
 表（四）Teacher
--- 
+
 | Tno  | Tname | Tsex | Tbirthday | Prof   |
 | ---- | ----- | ---- | --------- | ------ |
 | 804  | 李诚  | 男   | 1958-12-2 | 副教授 |
@@ -190,77 +189,233 @@ insert into Teacher values
     (825,'王萍','女','1972-5-5','助教','计算机系'),
     (831,'刘冰','女','1977-8-14','助教','电子工程系');
 ```
-3. **数据库中的数据**:
+3. 查询
 -- 
-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/
 
 ```sql
-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
-
-```sql
-select Teacher.Tno,Tname,Tsex,Tbirthday,Prof,Depart 
-from Teacher left join Course on Teacher.Tno = Course.Tno 
-left join Score on Course.Cno = Score.Cno 
-where Score.Sno is null;
-```
+-- 3. 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/
 
-
-4. 查询
--- 
-```sql
+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
+	
+SELECT
+	Teacher.Tno,
+	Tname,
+	Tsex,
+	Tbirthday,
+	Prof,
+	Depart 
+FROM
+	Teacher
+	LEFT JOIN Course ON Teacher.Tno = Course.Tno
+	LEFT JOIN Score ON Course.Cno = Score.Cno 
+WHERE
+	Score.Sno IS NULL;
+	
 -- 1　查询Score表中的最高分的学生学号和课程号。
-select Sno 学号,Cno 课程号 from Score
-where Degree = (select max(Degree) from Score);
+
+SELECT
+	Sno 学号,
+	Cno 课程号 
+FROM
+	Score 
+WHERE
+	Degree = ( SELECT max( Degree ) FROM Score );
+	
 -- 2　查询所有学生的Sname、Cno和Degree列。
-select Sname,Cno,Degree 
-from Student inner join Score on Student.Sno = Score.Sno;
+
+SELECT
+	Sname,
+	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 Sno,Cname,Degree from Score inner join Course on Score.Cno = Course.Cno;
+
+SELECT
+	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,Course,Score where Student.Sno=Score.Sno and Course.Cno=Score.Cno;
+
+SELECT
+	Sname,
+	Cname,
+	Degree 
+FROM
+	Student,
+	Course,
+	Score 
+WHERE
+	Student.Sno = Score.Sno 
+	AND Course.Cno = Score.Cno;
+	
 -- 5　查询“95033”班学生的平均分。
-select avg(Degree) from Score inner join Student on Score.Sno=Student.Sno where class=95033;
+
+SELECT
+	class,
+	avg( Degree ) 
+FROM
+	Score
+	INNER JOIN Student ON Score.Sno = Student.Sno 
+WHERE
+	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。
-select * from Score where Degree>(select Degree from Score where Sno = '109' and Cno = '3-105' ) and Cno = '3-105';
+
+SELECT * FROM Score WHERE Degree >( SELECT Degree FROM Score WHERE Sno = '109' AND Cno = '3-105' ) 
+AND 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。
-select * from Score a where Degree <(select MAX(degree) from Score b where a.Cno=b.Cno) and Sno in(select Sno from Score group by Sno having count(*)>1);
+
+SELECT * FROM Score a WHERE Degree <(SELECT MAX( degree ) FROM Score b WHERE a.Cno = b.Cno ) 
+AND Sno IN ( SELECT Sno FROM Score GROUP BY Sno HAVING count(*)> 1 );
+
 -- 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。
-select * from Score where Degree >(select Degree from Score where Sno='109' and Cno='3-105');
+
+SELECT * FROM Score WHERE Degree >( SELECT Degree FROM Score WHERE Sno = '109' AND 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。
-select Sno,Sname,Sbirthday from Student where Sbirthday=(select Sbirthday from Student where Sno='108');
+
+SELECT Sno, Sname, Sbirthday FROM Student WHERE Sbirthday =( SELECT Sbirthday FROM Student WHERE Sno = '108' );
+
 -- 10　查询“张旭“教师任课的学生成绩。
--select Sno,Degree from Score where Cno=(select Cno from Course inner join Teacher ON Course.Tno= Teacher.Tno where Tname='张旭' );
+
+SELECT
+	Sno,Degree 
+FROM
+	Score 
+WHERE
+	Cno =(
+	SELECT
+		Cno 
+	FROM
+		Course
+		INNER JOIN Teacher ON Course.Tno = Teacher.Tno 
+	WHERE
+		Tname = '张旭' 
+	);
+	
 -- 11　查询选修某课程的同学人数多于5人的教师姓名。
-select Tname from Teacher where Tno=(select Tno from Course where Cno=(select Cno from Score group by Cno having COUNT(Cno)>5));
+
+SELECT Tname FROM Teacher WHERE Tno =( SELECT Tno FROM Course WHERE Cno =( SELECT Cno FROM Score GROUP BY Cno HAVING COUNT( Cno )> 5 ));
+
 -- 12　查询出“计算机系“教师所教课程的成绩表。
-select sno,Cno ,Degree from Score where Cno in
-(select Cno from Course where Tno IN (select Tno from Teacher where Depart='计算机系'));
+
+SELECT
+	sno,Cno,Degree 
+FROM
+	Score 
+WHERE
+	Cno IN (
+	SELECT
+		Cno 
+	FROM
+		Course 
+	WHERE
+	Tno IN ( SELECT Tno FROM Teacher 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 from Teacher where Tno=(select Tno from Course where Cno=(select Cno from Score group by Cno having COUNT(Cno)>5));
+
+SELECT
+	Tname,prof 
+FROM
+	Teacher 
+WHERE prof in (SELECT Prof FROM Teacher WHERE Teacher.Depart = '计算机系' ) xor prof in ( SELECT Prof FROM Teacher WHERE Teacher.Depart = '电子工程系' );
+
 -- 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。
-select Cno,Sno,Degree from Score where Cno='3-105' and Degree>(select max(Degree) from Score where Cno= '3-245');
+
+SELECT Cno, Sno, Degree FROM Score WHERE Cno = '3-105' AND Degree >( SELECT max( Degree ) FROM Score WHERE Cno = '3-245' );
+
 -- 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.
-select Cno,Sno,Degree from Score where Cno='3-105' and Degree>(select max(Degree) from Score where Cno= '3-245');
+
+SELECT Cno, Sno, Degree FROM Score WHERE Cno = '3-105' AND Degree >( SELECT max( Degree ) FROM Score WHERE Cno = '3-245' );
+
 -- 16　查询成绩比该课程平均成绩低的同学的成绩表。
-select Cno,Sno,Degree from Score where Degree > avg(sum(select Degree from Score where Cno='3-245'));
+
+SELECT
+	* 
+FROM
+	Score a 
+WHERE
+	Degree < ( SELECT avg( Degree ) FROM score b WHERE a.Cno = b.Cno );
+	
 -- 17　查询所有任课教师的Tname和Depart.
-select Tname,Depart from Teacher;
+
+SELECT
+	Tname,Depart 
+FROM
+	Teacher;
+	
 -- 18　查询所有未讲课的教师的Tname和Depart.
-select Tname,Depart from Teacher left join Course on Teacher.Tno=Course.Tno left join Score on Course.Cno=Score.Cno where Score.Cno is null;
+
+SELECT
+	Tname,
+	Depart 
+FROM
+	Teacher
+	LEFT JOIN Course ON Teacher.Tno = Course.Tno
+	LEFT JOIN Score ON Course.Cno = Score.Cno 
+WHERE
+	Score.Cno IS NULL;
+	
 -- 19　查询“男”教师及其所上的课程。
-select Tname,Depart from Teacher where Tsex = '男';
+
+SELECT
+	Tname,Depart 
+FROM
+	Teacher 
+WHERE
+	Tsex = '男';
+	
 -- 20　查询最高分同学的Sno、Cno和Degree列。
-select Sno,Cno,degree from Score where Degree = (select max(Degree) from Score);
+
+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.
-select Sname from Student where Ssex=(select Ssex from Student where Sname ='李军');
+
+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')
+
+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。
-Select * from Score where Sno in (select Sno from Student where Ssex ='男')
-and Cno = (select Cno from Course where Cname='计算机导论');
+
+SELECT
+	* 
+FROM
+	Score 
+WHERE
+	Sno IN ( SELECT Sno FROM Student WHERE Ssex = '男' ) 
+	AND Cno = ( SELECT Cno FROM Course WHERE Cname = '计算机导论' );
 ```
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diff --git "a/06 \346\236\227\346\231\237\350\276\211/20230301\345\255\220\346\237\245\350\257\242\347\254\224\350\256\260.md" "b/06 \346\236\227\346\231\237\350\276\211/20230301\345\255\220\346\237\245\350\257\242\347\254\224\350\256\260.md"
new file mode 100644
index 0000000..494715c
--- /dev/null
+++ "b/06 \346\236\227\346\231\237\350\276\211/20230301\345\255\220\346\237\245\350\257\242\347\254\224\350\256\260.md"	
@@ -0,0 +1,25 @@
+# 一、笔记
+
+## 	1、select中嵌套子查询
+
+​		嵌套在另一个SQL语句中的查询，select语句可以嵌套在另一个select中，update，delete，insert，create等语句也可以，通常使用与where或having中
+
+## 	2、 SELECT的WHERE或HAVING中嵌套子查询
+
+​		如果子查询作为另一个SQL的过滤条件，通常把子查询嵌入到where或having中。
+
+根据子查询结果不同可以分为三种情况
+
+- 如果子查询是单列单值可以用比较运算符进行比较
+- 如果子查询是单列多值可以用in或者not in进行比较
+- 如果子查询是多列多值还可以用比较运算符搭配any、some、all等进行查询
+
+## 	3、select中嵌套exists型子查询
+
+​		exists型子查询是可以存在外层select的where子句中，不过它和上面的where型子查询的工作模式不一样
+
+​		如果exists关键字后面的参数是任意一个子查询，系统会对子查询进行运算用来判断他要不要返回行，如果至少返回一行，那么exists的结果位true，那么外层查询语句进行查询，反之如果没有返回行，那么exists结果为false，外层查询语句不进行查询，exists和not exists的结果只取决于是否返回行不取决于这些行的内容。
+
+​		如果exists关键字后面的参数是一个关联子查询，那么子查询的where条件中包含与外层查询表的关联条件，那么此时将对外层查询表做循环，即在筛选外层查询表的每一条记录都看是否满足子查询的条件，如果满足那么就用外层进行二次筛选，否则丢弃这行记录。
+
+​		
\ No newline at end of file
-- 
Gitee