2. Primary keys
A table can only have one primary key. A primary key is a field or set
of fields that:
•Has a unique value for each record
•Is indexed
•Identifies the record
• It uniquely defines a relationship within a database.
• It is a field or a combination of two or more fields. The value in the
primary key field for each record uniquely identifies that record.
Specify Primary Keys

3. Foreign keys
A foreign key, simply stated, is another table's primary key. The values
in a foreign key field match values in the primary key, indicating that
the two records are related — for example, a customer and an order
that she has placed. Unlike primary keys:
•A table can have more than one foreign key.
•A foreign key does not necessarily have unique values.
Specify Foreign Keys

4. •A foreign key cannot reliably identify a particular record. For example, you
cannot always tell which record you are viewing from the Orders table by
looking at the Customer ID.
You create a foreign key when you use the Lookup Wizard to create a field.
Specify Foreign Keys

5. For example, each customer might have
many orders. Rather than store the
customer's address in each record in the
Orders table, you store that information
once in a record in the Customers table. To
combine the customer information with the
rest of the information about the order, you
create a relationship between the two
tables, by using key fields.
You can add the primary key from one table to another table to
create a relationship between them. In the other table, it is called a
foreign key.
For example, suppose you use the primary key of the Customers
table in the Orders table. In the Orders table it is a foreign key.

6. Legend:
1 Primary Keys
2 Foreign Keys

7. Add records directly to a
table in datasheet view
A table open in Datasheet view resembles an Excel worksheet, and you
can type or paste data into one or more fields — the equivalent of a cell in
a worksheet.

8. Remember these facts as you proceed.
 You do not need to explicitly save your data. Access commits your
changes to the table when you move the cursor to a new field in the
same row, or when you move the cursor to another row.
 By default, the fields in an Access database are set to accept a specific
type of data, such as text or numbers. You must enter the type of data
that the field is set to accept. If you don't, Access displays an error
message:
 A field may have an input mask applied. An input mask is a set of literal
and placeholder characters that force you to enter data in a specific
format.