UNIQUE Constraints

You can use UNIQUE constraints to enforce entity integrity on a non-primary key. Using a UNIQUE constraint also ensures that no duplicate values are entered.

    To create a UNIQUE constraint

• In SQL Enterprise Manager's Server Manager window, double-click the appropriate table, choose the Advanced Features button, and then choose the Unique Constraints tab.

  (For details, search for "constraints" in SQL Enterprise Manager Help.)

Or

• Use the CREATE TABLE or ALTER TABLE statement.

  For example:

  ALTER TABLE stores 
  ADD
  CONSTRAINT UNC_name_city UNIQUE NONCLUSTERED (stor_name, city)

  adds a UNIQUE constraint on the stor_name and city columns.

  (For details, see the CREATE TABLE and ALTER TABLE statements in the Microsoft SQL Server Transact-SQL Reference.)