Difference Between Primary Key and Unique Key in SQL

Difference Between Primary Key and Unique Key 

	Primary Key	Unique Key
1	Primary Key Can't Accept Null Values.	Unique Key Can Accept Only One Null Value
2	Creates Clustered Index	Creates Non-Clustered Index
3	Only One Primary key in a Table	More than One Unique Key in a Table.
4	Primary Key Can be Made Foreign Key Into Another Table. Ex: CREATE TABLE [country] (        [id]    VARCHAR (50) NOT NULL,     [country] VARCHAR (50) NOT NULL,          CONSTRAINT [PK_country] PRIMARY KEY CLUSTERED ([id]));	SQL Server, Unique Key Can be Made Foreign Key Into Another Table. Ex: CREATE TABLE [country] (         [name]    VARCHAR (50) NOT NULL,     [country] VARCHAR (50) NOT NULL,       UNIQUE NONCLUSTERED ([name]));

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Set Primary Key,Unique Key,Foreign Key Sql Server Database Table in Visual Studio

Set Primary Key,Unique Key,Foreign Key


Set to Primary Key ,Foreign Key , Unique Key Sql Server DataBase Table Fields  Using Visual Studio


                                 DEMO

Primary Key


     CREATE TABLE [dbo].[country] (

    [id]      INT          IDENTITY (1, 1) NOT NULL,

    [name]    VARCHAR (50) NOT NULL,

    [country] VARCHAR (50) NOT NULL,

    [amount]  VARCHAR (50) NOT NULL,

    

   CONSTRAINT [PK_country] PRIMARY KEY CLUSTERED ([id] ASC),

   

  );

Unique Key

CREATE TABLE [dbo].[country] (

    [id]      INT          IDENTITY (1, 1) NOT NULL,

    [name]    VARCHAR (50) NOT NULL,

    [country] VARCHAR (50) NOT NULL,

    [amount]  VARCHAR (50) NOT NULL,

    CONSTRAINT [PK_country] PRIMARY KEY CLUSTERED ([id] ASC),

    UNIQUE NONCLUSTERED ([name] ASC)

);

Foreign Key

CREATE TABLE [dbo].[register] (

    [username] VARCHAR (50) NOT NULL,

    [password] VARCHAR (50) NOT NULL,

    [country]  VARCHAR (50) NOT NULL,

    [name]     VARCHAR (50) NOT NULL,

    CONSTRAINT [FK_reg_country] FOREIGN KEY ([name]) REFERENCES [dbo].[country] ([name])

);

First - Add - New Web Form - Create Database Tables - Fields 

Next - Set Primary Key To id Field - Select Field - Right Click - Set Primary Key

Next - Unique Key - Assign - name Field

Next - Assign Another Table - Same Field of Unique Field Set Foreign Key

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