Primary Key Constraints

A primary key constraint ensures no duplicate values are entered in particular columns and that NULL values are not entered in those columns. You can use primary key constraints to enforce uniqueness as well as referential integrity. For example, the au_id column uniquely identifies each author stored in the authors table.

You create primary key constraints directly in a database diagram.

To	See
Enforce uniqueness for values entered in specified columns	Defining a Primary Key
Change the column order, index name, clustered option, or fill factor	Modifying a Primary Key
Copy column properties from a primary key column to a foreign key column to relate the two columns	Copying Column Properties to a Foreign Key Column
Remove the requirement for uniqueness for the values entered in a column	Deleting a Primary Key Constraint