1.数据库的相关概念 数据(Data)数据就是客观信息的一种描述 数据库(DataBase) 指长期存储在计算机内有组织、可共享的数据集合。 数据库管理系统(DataBase Management System) 为数据库建立、使用和维护而配置的软件。 数据库系统(DataBase System) 在计算机
1.数据库的相关概念
数据(Data) 数据就是客观信息的一种描述
数据库(DataBase)
指长期存储在计算机内有组织、可共享的数据集合。
数据库管理系统(DataBase Management System)
为数据库建立、使用和维护而配置的软件。
数据库系统(DataBase System)
在计算机系统中引入数据库后的系统构成。
2.数据的冗余
同一数据反复存放
问题：浪费存储空间、更新数据容易出错。
数据库不一致性
同一数据在不同地方有不同的值
3.数据库的系统模型
数据库系统根据数据存储的数据模型可以分为：
层次性数据库
网状型数据库
关系型数据库
面向对象型数据库
4.数据库概念模型
基本概念：
实体：客观存在并可以相互区分的事物就叫实体
属性：实体的特性，美国服务器，通过属性来对实体进行描述
键、主键、外键：一个属性或者多个属性构成的子集合能够唯一标识整个属
5.为什么需要设计数据库
良好的数据库设计
节省数据的存储空间
能够保证数据的完整性
方便进行数据库应用系统的开发
糟糕的数据库设计
数据冗余、存储空间浪费
内存空间浪费
数据更新和插入的异常
6.软件项目开发周期
需求分析--实地调查
概念结构设计--实体模型
逻辑结构模型--逻辑模型
物理结构设计--物理模型
数据库实施--数据库的运用和调试
7.实体之间的关系
实体之间的关系
一对一
一对多
多对多
8.表示实体间的关系
E-R图
9.三大范式
第一范式的目标是确保每列的原子性
如果每列都是不可再分的最小数据单元（也称为最小的原子单元），则满足第一范式（1NF）
第二范式 (2nd NF)
如果一个关系满足1NF，并且除了主键以外的其他列，都依赖与该主键，则满足第二范式（2NF）
第二范式要求每个表只描述一件事情
第三范式 (3rd NF)
如果一个关系满足2NF，并且除了主键以外的其他列都不传递依赖于主键列，则满足第三范式（3NF）
10.数据库的设计规范是什么？
为了设计结构良好的数据库，需要遵守一些专门的规则，美国空间，称为数据库的设计范式。
11.可以分为那几范式？
第一范式（1NF）的目标：确保每列的原子性。
第二范式（2NF）的目标：确保表中的每列，都和主键相关 。
第三范式（3NF）的目标：确保每列都和主键列直接相关，而不是间接相关 。
12.什么是数据库？
长期存储在计算机内，有组织、可共享的数据集合
13.实体之间的关系有哪些？
一对一、一对多、多对多
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