Set or change the primary key

1. Open a table in Design view.
   
   
2. Select the field or fields you want to define as the primary key.

   To select one field, click the row selector for the desired field.

   To select multiple fields, hold down the CTRL key and then click the row selector for each field.

3. Click Primary Key on the toolbar.

For more information on how to choose a primary key, click .

Notes

• You can specify a primary key for a field that already contains data, but Microsoft Access generates a message when you save the table if it finds duplicate values or Null values in the field. If you encounter this message, you have three choices: use a Find Duplicates query to locate records with duplicate values or Null values and then edit the field to remove them; choose a different field; or add an AutoNumber field and set it as the primary key. For more information on finding duplicate records, click .
  
  
• In a multiple-field primary key, field order may be important to you. The fields in a multiple-field primary key are sorted according to their order in table Design view. If you want a different order, first specify the fields for the primary key as described in the preceding procedure, and then click Indexes on the toolbar to display the Indexes window and reorder the field names for the index named PrimaryKey.