Prevent duplicate values from being entered into a field

A single-field primary key prohibits duplicate values in that field to ensure that each record has a unique identifier. However, you may want to prevent duplicate values in other fields as well. For example, you might want to assign computers to employees using a serial number field for the computers.

1. Open a table in Design view.
   
   
2. In the upper portion of the window, click the field that you want to prohibit duplicate values for.
   
   
3. In the lower portion of the window on the General tab, click in the Indexed property box, and then click Yes (No Duplicates).

To find out how to prevent duplicate entries in a combination of fields, click .