Difference Between Primary Key and Unique Key

Primary Key and Unique Key

1) Only 1 Primary key can be defined in one table while as unique key can be defined more than 1 in a table

2) Primary never accept null value while as the Unique key can accept multiple null values

3) On the creation of Primary Key, a clustered index created on the table while as On the creation of Unique Key, a non-clustered index created on the table

4) The primary key is used for identifying a record while a Unique key is used to prevent duplicate records in a table

Primary Key:

• There can only be one primary key in a table
• In some DBMS it cannot be NULL - e.g. MySQL adds NOT NULL
• Primary Key is a unique key identifier of the record

Unique Key:

• Can be more than one unique key in one table
• Unique key can have NULL values
• It can be a candidate key
• Unique key can be NULL and may not be unique

 

 

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About Mariano

I'm Ethan Mariano a software engineer by profession and reader/writter by passion.I have good understanding and knowledge of AngularJS, Database, javascript, web development, digital marketing and exploring other technologies related to Software development.