Primary Key

• A primary key, also called a primary keyword, is akey in a relational database that is unique for each record. It is a unique identifier, such as a driver license number, telephone number (including area code), or vehicle identification number (VIN). A relational database must always have one and only one primary key.
• A primary key field is an index that greatly speeds up queries, searches and sort requests.
• When you add new records, you must enter a value in the primary key field(s). Microsoft Access will not allow you to enter Null values, which guarantees that you will have only valid records in your table.
• When you add new records to a table that has a primary key, Microsoft Access checks for duplicate data and doesn't let you enter duplicates for the primary key field.
• By default, Access displays your data in the order of the primary key.
• Primary key fields should be made as short as possible as this can affect the speed of operations in the database.