Difference between Primary Key and Unique Key

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SQL-Server

Hi,
Any one please explain the difference between Primary and unique keys with an example.

Posted 27-Sep-13 0:20am

DileepReddyC

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ArunRajendra · Accepted Answer · 2013-09-27T00:22:00

The only difference is unique can contain one null value where as primary key cannot contain any null.

Unique Example:
1
2
NULL
3
4
NULL (This will throw constraint violation error as it will be duplicate)
4 (This will also throw constraint violation error as it will be duplicate)

Primary key Example:
1
2
NULL (This will throw constraint violation error)
3
4
4 (This will also throw constraint violation error as it will be duplicate)

codestar007 · Accepted Answer · 2013-09-27T00:25:00

Solution 2

difference-between-primary-key-and-unique-key-in-sql-server/[^]

difference-between-primary-key-and.html[^]

Check the above links
else google[^] is best place to get help..

Posted 27-Sep-13 0:25am

codestar007

Comments

DileepReddyC 27-Sep-13 6:31am

thank u

[no name] 27-Sep-13 6:33am

Welcome..please accept the solution if it's helpful.so that it will be helpful for others..