Difference Between Primary Key and Foreign Key
| Primary Key | Foreign Key | |
| 1 |
Primary Key Can Not Accept Null Values.
|
Foreign Key Can Accept Multiple Null Values.
|
| 2 |
Only One Primary Key in a Table.
|
More than One Foreign Key in a Table.
|
| 3 |
Primary Key Uniquely Identify a Record in the Table
|
Foreign Key is a Field in the Table that is Primary Key in Another Table
|
| 4 |
Primary Key is Clustered Index.
Ex:
CREATE TABLE [country] (
[id]
INT IDENTITY (1, 1) NOT NULL,
[name] VARCHAR
(50) NOT NULL,
UNIQUE NONCLUSTERED ([name],
CONSTRAINT [PK_country] PRIMARY KEY CLUSTERED ([id])
);
|
Foreign Key is Non-Clustered Index.
Ex:
CREATE TABLE [reg] (
[country]
VARCHAR (50) NOT NULL,
[name]
VARCHAR (50) NOT NULL,
CONSTRAINT [FK_reg_country] FOREIGN KEY ([name]) REFERENCES [dbo].[country] ([name])
);
|
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