Unique Constraints

A unique constraint ensures no duplicate values are entered into specified columns that are not a table's primary key. For example, in the employee table in which the emp_id column is the primary key, you can define a unique constraint that requires entries in the Social Security number (ssn) column to be unique within the table.

In database diagrams, you use the Indexes/Keys property page to create, modify, or delete unique constraints.

To	See
Ensure no duplicate values are entered in specific columns	Creating a Unique Constraint
Change the columns that the constraint is attached to, change the constraint name, or set additional properties for the constraint	Modifying a Unique Constraint
Remove the requirement for uniqueness for values entered in the column	Deleting a Unique Constraint