<s>
AutoNumber	B-Operating_System
is	O
a	O
type	O
of	O
data	O
used	O
in	O
Microsoft	B-Application
Access	I-Application
tables	O
to	O
generate	O
an	O
automatically	O
incremented	O
numeric	O
counter	O
.	O
</s>
<s>
It	O
may	O
be	O
used	O
to	O
create	O
an	O
identity	B-Language
column	I-Language
which	O
uniquely	O
identifies	O
each	O
record	O
of	O
a	O
table	O
.	O
</s>
<s>
Only	O
one	O
AutoNumber	B-Operating_System
is	O
allowed	O
in	O
each	O
table	O
.	O
</s>
<s>
There	O
are	O
three	O
forms	O
in	O
which	O
AutoNumbers	B-Operating_System
can	O
be	O
generated	O
:	O
</s>
<s>
start	O
value	O
plus	O
increment	O
AutoNumbers	B-Operating_System
generated	O
by	O
this	O
mechanism	O
start	O
with	O
the	O
start	O
number	O
and	O
increment	O
with	O
the	O
increment	O
value	O
,	O
checking	O
for	O
collision	O
with	O
existing	O
table	O
rows	O
.	O
</s>
<s>
random	O
AutoNumbers	B-Operating_System
generated	O
by	O
this	O
mechanism	O
are	O
assigned	O
using	O
a	O
pseudo-random	B-Algorithm
number	I-Algorithm
generator	I-Algorithm
that	O
generates	O
long	O
integers	O
and	O
checks	O
for	O
collisions	O
with	O
existing	O
table	O
rows	O
.	O
</s>
<s>
replication	O
IDs	O
AutoNumbers	B-Operating_System
generated	O
by	O
this	O
mechanism	O
are	O
IDs	O
generated	O
in	O
a	O
manner	O
to	O
make	O
it	O
highly	O
improbable	O
that	O
collisions	O
will	O
occur	O
.	O
</s>
<s>
The	O
default	O
size	O
of	O
an	O
AutoNumber	B-Operating_System
is	O
a	O
4-byte	O
(	O
long	O
)	O
integer	O
.	O
</s>
<s>
This	O
is	O
the	O
size	O
used	O
for	O
start+increment	O
and	O
random	O
AutoNumbers	B-Operating_System
.	O
</s>
<s>
For	O
replication	O
ID	O
AutoNumbers	B-Operating_System
,	O
the	O
FieldSize	O
property	O
of	O
the	O
field	O
is	O
changed	O
from	O
long	O
integer	O
to	O
Replication	O
ID	O
.	O
</s>
<s>
If	O
an	O
AutoNumber	B-Operating_System
is	O
a	O
long	O
integer	O
,	O
the	O
NewValues	O
property	O
determines	O
whether	O
it	O
is	O
of	O
the	O
start+increment	O
or	O
random	O
form	O
.	O
</s>
<s>
The	O
default	O
AutoNumber	B-Operating_System
type	O
is	O
a	O
start+increment	O
counter	O
,	O
with	O
a	O
start	O
value	O
of	O
1	O
and	O
an	O
increment	O
of	O
1	O
.	O
</s>
<s>
Although	O
in	O
many	O
instances	O
such	O
an	O
AutoNumber	B-Operating_System
field	O
will	O
appear	O
as	O
if	O
it	O
contains	O
the	O
row	O
count	O
,	O
it	O
does	O
not	O
.	O
</s>
<s>
Deletion	O
of	O
rows	O
from	O
a	O
table	O
,	O
for	O
example	O
,	O
does	O
not	O
cause	O
AutoNumber	B-Operating_System
fields	O
to	O
be	O
re-numbered	O
,	O
but	O
instead	O
leaves	O
"	O
holes	O
"	O
in	O
the	O
numbering	O
.	O
</s>
<s>
Similarly	O
,	O
if	O
a	O
transaction	O
to	O
add	O
a	O
row	O
to	O
a	O
table	O
is	O
begun	O
but	O
later	O
aborted	O
,	O
the	O
AutoNumber	B-Operating_System
assigned	O
for	O
that	O
row	O
will	O
not	O
be	O
re-used	O
.	O
</s>
<s>
For	O
example	O
,	O
using	O
an	O
AutoNumber	B-Operating_System
field	O
for	O
a	O
customer	O
ID	O
might	O
reveal	O
information	O
that	O
it	O
is	O
desirable	O
not	O
to	O
reveal	O
to	O
,	O
say	O
,	O
customer	O
number	O
6	O
.	O
</s>
<s>
This	O
is	O
one	O
example	O
of	O
occasion	O
where	O
the	O
start	O
value	O
of	O
an	O
AutoNumber	B-Operating_System
field	O
is	O
raised	O
,	O
so	O
that	O
customer	O
number	O
6	O
has	O
,	O
say	O
,	O
AutoNumber	B-Operating_System
field	O
value	O
10006	O
.	O
</s>
<s>
A	O
common	O
problem	O
with	O
AutoNumber	B-Operating_System
fields	O
is	O
encountered	O
if	O
tables	O
are	O
replicated	O
.	O
</s>
<s>
If	O
multiple	O
users	O
are	O
using	O
multiple	O
replicas	O
of	O
the	O
table	O
,	O
then	O
it	O
is	O
likely	O
that	O
they	O
will	O
end	O
up	O
assigning	O
the	O
same	O
values	O
to	O
AutoNumber	B-Operating_System
fields	O
in	O
new	O
rows	O
that	O
they	O
add	O
,	O
causing	O
replication	O
conflicts	O
when	O
the	O
replicas	O
are	O
merged	O
.	O
</s>
<s>
First	O
,	O
it	O
is	O
possible	O
to	O
use	O
Replication	O
IDs	O
for	O
such	O
AutoNumbers	B-Operating_System
.	O
</s>
<s>
Second	O
,	O
when	O
Access	O
creates	O
table	O
replicas	O
,	O
it	O
automatically	O
changes	O
AutoNumbers	B-Operating_System
of	O
the	O
start+increment	O
form	O
to	O
the	O
random	O
form	O
.	O
</s>
<s>
The	O
following	O
Data	B-Language
Definition	I-Language
Language	I-Language
(	O
DDL	O
)	O
query	O
creates	O
an	O
AutoNumber	B-Operating_System
field	O
with	O
a	O
start	O
value	O
and	O
an	O
increment	O
:	O
</s>
