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Difference between Primary Key and Unique Key

By default, primary key creates clustered index on the column and then enforces the uniqueness of the column whereas the unique key, by default creates a non-clustered index.

Primary Key

  • By default, creates Clustered index
  • Doesn’t allow null
  • Table can have only one Primary Key ( Can include multiple columns together )

Unique Key

  • By default, creates non clustered index
  • Accepts null value
  • Table can have many unique keys
Senthil Kumar B
Senthil Kumar is a former Microsoft MVP (Most Valuable Professional). He is a Co-Author of the book "Windows 10 Development Recipes using JavaScript and CSS" for Apress Publication. He is a technical presenter, blogger, mentor and a Geek.  Senthil is a regular speaker is various local user groups. He has presented at conferences like Great Indian Developer Summit (GIDS) & Microsoft DevCamps. You can reach out to him via his Twitter handle @isenthil.