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Sunday, 19 June 2016

Difference Between Primary Key and Unique Key In Sql Server Table

6/19/2016 - By Pranav Singh 0

This article will show what exactly difference between primary key and the unique in sql server. In this I will share the information about primary key and unique key and then define.
Primary key:
  •   A primary key on a sql table is a field is uniquely identifies each record in a database table.
  •  Primary key column always contain values.
  • Primary key column value cannot have NULL values.
  • A table can have only one primary key, which may consist of single or multiple fields.
Unique Key:
  • A unique key on a sql table is a field is uniquely identifies each record in a database table.
  • Unique key column can have only one NULL value.

Difference between Primary Key and Unique Key

PRIMARY KEY
UNIQUE KEY
It have uniquely identifies values without null value
It have uniquely identifies values with only one null value
Table column can have only one Primary key in a table
Table column can have only one Unique key in a table.
By default primary key adds a clustered index
By default unique key adds a non-clustered index
Primary key can be made foreign key into another table.
Unique key can be made foreign key into another table in sql server.

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