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Date: Thu, 7 Sep 2023 12:35:47 +0800
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+## 笔记
+
+### 数据库
+关系是相互的，一个学生，可以选多个课，课也可以被多个学生选(多对多)这种关系应借助第三个表进行关联，将前面两张表的主键当作外键表与表的关系:1对1，1对多，多对多
+1对多:第二张的表的主键当另一个表的外键(多)
+(1)	当1对1:将其中任一表的主键放在另一张表中的外键
+头脑风暴:院系、专业、班级、学生，教师、谢程、深程表、教室visio
+链头变上有一个号数据库chen's
+数据库设计方法	按住(f11，再抢动，可复制	
+1.直观设计法	选中，一直抢动，不能点击	
+2.规范设计法	多对多，用字日表行N.M…	
+3.算机辅助设计法		
+E-R图(实体关系图)
+3要表:实体(表)、属性(字段)和关系(类似外键约束)
+实体：用矩形.主键:加下划线 外键:横线中间加菱形
+
+
+
+### mysql
+
+``` mysql
+CREATE DATABASE yangyang charset utf8;
+use yangyang;
+##学院表
+CREATE table college(   
+collegeName VARCHAR(12),
+collegeId int PRIMARY key
+);
+
+##专业表
+CREATE TABLE major(
+majorId int PRIMARY key,
+majorName VARCHAR(12),
+collegeId int,
+foreign KEY (collegeId) references college(collegeId)
+);
+
+##班级表
+CREATE TABLE class(
+classId int PRIMARY key,
+className VARCHAR(12),
+majorId int,
+foreign KEY (majorId) references major(majorId)
+);
+#3教室表
+CREATE TABLE classroom(
+classroomId int PRIMARY key ,
+classroomAddress VARCHAR(12),
+classroomName VARCHAR(12)
+);
+
+##教师表
+CREATE TABLE teacher(
+teacherId int PRIMARY  key,
+teacherName VARCHAR(12),
+courseld int
+);
+DROP TABLE student;
+
+##学生表
+CREATE TABLE student(
+studentId int PRIMARY  key,
+studentName VARCHAR(12),
+sex CHAR,
+courseId int
+);
+drop TABLE course;
+## 课程表
+CREATE TABLE course(
+courseId int PRIMARY key,
+courseName VARCHAR(12),
+classroomId int,
+teacherId int,
+studentId int,
+classId int,
+foreign KEY (classId) references class(classId),
+foreign KEY (classroomId) references classroom(classroomId),
+foreign KEY (teacherId) references teacher(teacherId),
+foreign KEY (studentId) references student(studentId)
+);
+
+```
+
+
+
+```mysql
+CREATE DATABASE yangyang charset utf8;
+use yangyang;
+##学院表
+CREATE table college(   
+collegeName VARCHAR(12),
+collegeId int PRIMARY key
+);
+
+INSERT into college VALUES
+ ('软件工程学院'，1),
+ ('信息技术学院'，2),
+ ('软件工程学院'，3);
+
+
+##专业表
+CREATE TABLE major(
+majorId int PRIMARY key,
+majorName VARCHAR(12),
+collegeId int,
+foreign KEY (collegeId) references college(collegeId)
+);
+
+INSERT into major VALUES
+(1,'软件技术',1),
+(2,'软件技术',2),
+(3,'软件技术',3);
+
+##班级表
+CREATE TABLE class(
+classId int PRIMARY key,
+className VARCHAR(12),
+majorId int,
+foreign KEY (majorId) references major(majorId)
+);
+#3教室表
+CREATE TABLE classroom(
+classroomId int PRIMARY key ,
+classroomAddress VARCHAR(12),
+classroomName VARCHAR(12)
+);
+
+##教师表
+CREATE TABLE teacher(
+teacherId int PRIMARY  key,
+teacherName VARCHAR(12),
+courseld int
+);
+DROP TABLE student;
+
+##学生表
+CREATE TABLE student(
+studentId int PRIMARY  key,
+studentName VARCHAR(12),
+sex CHAR,
+courseId int
+);
+drop TABLE course;
+## 课程表
+CREATE TABLE course(
+courseId int PRIMARY key,
+courseName VARCHAR(12),
+classroomId int,
+teacherId int,
+studentId int,
+classId int,
+foreign KEY (classId) references class(classId),
+foreign KEY (classroomId) references classroom(classroomId),
+foreign KEY (teacherId) references teacher(teacherId),
+foreign KEY (studentId) references student(studentId)
+);
+
+
+```
+
-- 
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