How to set the primary key in access?
If you have a table where each record has a unique identifying number (such as an ID number, serial number, or encoding), this field can make a good primary key. For a primary key to work properly, the field must uniquely identify each row, never contain a null or Null value, and rarely (ideally never) change.
To set the primary key explicitly, you must use Design view. Click the Office Button, and then click Open. In the Open dialog box, select and open the database. In the Navigation Pane, right-click the table on which you want to set the primary key, and then on the shortcut menu, click Design View. Select one or more fields to use as primary keys. To select a field, click the row selector for the desired field.
To select multiple fields, hold down Ctrl and click the row selector for each field. On the Design tab, in the Tools group, click Primary Key. A key indicator is added to the left of the field or fields that you specify as primary keys.
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