1. Primary keysA table can only have one primary key. A primary
key is a field or setof fields that:Has a unique value for each
recordIs indexedIdentifies 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 theprimary key field for each
record uniquely identifies that record.Specify Primary Keys
2. Foreign keysA foreign key, simply stated, is another tables
primary key. The valuesin a foreign key field match values in the
primary key, indicating thatthe two records are related for
example, a customer and an orderthat 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 3. A
foreign key cannot reliably identify a particular record. For
example, youcannot always tell which record you are viewing from
the Orders table bylooking at the Customer ID.You create a foreign
key when you use the Lookup Wizard to create a field.Specify
Foreign Keys 4. For example, each customer might havemany orders.
Rather than store thecustomers address in each record in theOrders
table, you store that informationonce in a record in the Customers
table. Tocombine the customer information with therest of the
information about the order, youcreate a relationship between the
twotables, by using key fields.You can add the primary key from one
table to another table tocreate a relationship between them. In the
other table, it is called aforeign key.For example, suppose you use
the primary key of the Customerstable in the Orders table. In the
Orders table it is a foreign key. 5. Legend:1 Primary Keys2 Foreign
Keys 6. Add records directly to atable in datasheet viewA table
open in Datasheet view resembles an Excel worksheet, and youcan
type or paste data into one or more fields the equivalent of a cell
ina worksheet. 7. Remember these facts as you proceed. You do not
need to explicitly save your data. Access commits yourchanges to
the table when you move the cursor to a new field in thesame row,
or when you move the cursor to another row. By default, the fields
in an Access database are set to accept a specifictype of data,
such as text or numbers. You must enter the type of datathat the
field is set to accept. If you dont, Access displays an
errormessage: A field may have an input mask applied. An input mask
is a set of literaland placeholder characters that force you to
enter data in a specificformat.
