Microsoft Office Tutorials and References
In Depth Information
AutoNumber
Access Data Types
Figure 26-19:
Top: In this example,
Access notices that you’ve
updated the attachment
file “The Story of the
Count. doc” in Word.
When you close the
Attachments window, Access
asks if you want to update
the database with the new
saved version.
Bottom: This system only
works if you keep the
Attachments window open
while you edit. If you close
the Attachments window
while the attachment file
is still open, you get a
warning message like this
one. If you continue, then
any changes you make (or
any changes you’ve made
so far and haven’t saved)
won’t be reflected in the
database. (To avoid such
headaches, attach only
files that you don’t plan
to edit.)
AutoNumber
An AutoNumber is a special sort of data type. Unlike with all the other data types
you’ve seen, you can’t fill in the value for an AutoNumber field. Instead, Access
does it automatically whenever you insert a new record. Access makes sure that the
AutoNumber value is unique—in other words, it never gives two records the same
AutoNumber value.
Note: Every table can have up to one AutoNumber field.
Ordinarily, the AutoNumber field looks like a sequence of numbers—Access tends
to give the first record an AutoNumber value of 1, the second an AutoNumber of
2, and so on. However, the truth isn’t so straightforward. Sometimes, Access skips
a number. This skipping could happen when several people are using a database at
once, or if you start adding a new record, and then cancel your action by pressing
Esc. You may also delete an existing record, in which case Access never reuses that
 
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