SQL Server +复合键或唯一标识 [英] SQL Server + Composite key or Unique Id

问题描述

我对数据库设计相当新，对于多对多的关系，为

创建复合键和唯一id有什么区别和影响？ code>国家表

  CountryID 
 CountryName 
  

语言表

  LanguageID 
 LangugageName 
  

表 - 使用组合：

  CountryID Pkey 
 LanguageID Pkey 
  pre> 
 
 
或
 
 
 
使用唯一ID：
  AutoID Pkey 
 CountryID 
 LanguageID 
  
 
 
解决方案
 复合键： 
 
 
 
复合键是由多个列组成的，唯一的行在表中。 
复合键可以是主键。
 
 
 
  PRIMARY键 
 
 
 
 PRIMARY KEY约束唯一标识数据库表中的每个记录。
 
 
 
因此它取决于您的需求
 
 
 
 第一个设计 
 多对多表：
使用composite：
 CountryID Pkey 
 LanguageID Pkey 
  
 
 
如果使用此设置，CountryID和LanguageID是复合主key.ie此处
 
 
 
表格数据将为
  CountryId LaguageID 
 1 1 // valid 
 1 2 // valid 
 1 3 // valid 
 1 1 //无效的数据作为其形式复合主键
  
 
 
 
和第二个设计 
 使用唯一ID：
 AutoID Pkey 
 CountryID 
 LanguageID 
  
 AutoID成为主键，因此这将允许数据lke thsi 
  AutoId CountryId LaguageID 
 1 1 1 // valid 
 2 1 2 // valid 
 3 1 3 // valid 
 4 1 1 // valid as AutoID is primary key 
 1 2 3 / / invalid as AutoID is prinary key 
  
希望此演示文稿帮助您理解差异
 
I am fairly new to database design, for many to many relationship, what is the differences and implications of creating a composite key and a unique id for e.g.

Country table
CountryID
CountryName
Language table
LanguageID
LangugageName
Many to Many table - using composite:
CountryID  Pkey
LanguageID Pkey
OR

Using unique Id:
AutoID Pkey
CountryID 
LanguageID 

解决方案
Composite Key : 

A composite key is a combination of more than one column to identify a unique row in a table.
composite key can be a primary key .

PRIMARY KEY

The PRIMARY KEY constraint uniquely identifies each record in a database table.

so its all depend on your requirement 

in first design
Many to Many Table:
Using composite:
CountryID  Pkey
LanguageID Pkey
if you use this desing than CountryID  and LanguageID  is composite primary key.i.e here 

data of the table will be 
CountryId  LaguageID
  1           1 //valid
  1           2 //valid
  1           3 //valid
  1           1//not valid data as its form composite primary key
and in second design 
Using Unique Id:
AutoID Pkey
CountryID 
LanguageID 
AutoID  is become primary key so this will allow data lke thsi 
AutoId    CountryId  LaguageID
 1          1           1 //valid
 2          1           2 //valid
 3          1           3 //valid
 4          1           1 //valid as AutoID is primary key
 1          2           3 // invalid as AutoID is prinary key
hope this presentation help you to understand difference 

                        
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