Rules for Creating Primary Key in an Access 2007 Database
It doesn’t matter where you place a primary key in your table. It can be the first field, last field, or any field in between. Although Access 2007 doesn’t care where your primary key resides, you will find it much easier later on if you place your primary key in the first field of your table. This is especially true when you start creating relationships between and among tables.
By default, Access 2007 adds a primary key to every table you create. Even if you create a table in Design View without a primary key, Access 2007 will add a primary key to the table when you save the table. Access 2007’s default field name for a primary key is ID. If you desire, change this field name to anything you like. Something more descriptive may be more appropriate because “ID" could mean anything in most databases. Remember that you may not be the only person who uses this database so choose a name that makes it clear that the field contains a primary key.
There are some restrictions when creating primary keys. First, each table can only contain one primary key. There is no reason to uniquely identify a record with two keys because this would be redundant. Remember, a primary key identifies a record uniquely. There is no reason do this twice. Doing so would create problems later when you query or index the database.
Access 2007 allows for many field types such as memo, OLE object, and hyperlink. None of these field types can be used for a primary key. For example, you cannot use an embedded picture (OLE object) to uniquely identify a record. Nor can you use a hyperlink for the same purpose. Also, avoid using a yes/no field type for a primary key because then you would be restricted to only two records on the table, one record uniquely identified with a “yes" value and another record uniquely identified with a “no" value.