Concurrent Access - New Record, Primary Key problem....

Can someone explain what happens when two users concurrently attempt to
create a new record in a table with an autonumber primary key? For example,
user 1 creates a new record and manipulates it within a transaction making
use (perhaps) of the @.@.IDENTITY value when creating other, related records.
Before this transaction is complete, user 2 creates a new record and does
the same thing. Presumably they will both have the same @.@.IDENTITY? If
this is the case, how is it possible to manage such a situation?

Thanks."Robin Tucker" <idontwanttobespammedanymore@.reallyidont.com> wrote in
message news:csgov0$4e6$1$830fa17d@.news.demon.co.uk...
> Can someone explain what happens when two users concurrently attempt to
> create a new record in a table with an autonumber primary key? For
> example, user 1 creates a new record and manipulates it within a
> transaction making use (perhaps) of the @.@.IDENTITY value when creating
> other, related records. Before this transaction is complete, user 2
> creates a new record and does the same thing. Presumably they will both
> have the same @.@.IDENTITY? If this is the case, how is it possible to
> manage such a situation?
> Thanks.

No, each session will have a different value, so there's no problem with
concurrency - check out SCOPE_IDENTITY(), IDENT_CURRENT() and @.@.IDENTITY in
Books Online.

Note that just defining a column as an identity column is not enough to
guarantee uniqueness - you can still create duplicates manually (see SET
IDENTITY_INSERT in BOL), so if you want to use the column as a PK, make sure
it is declared as a PK when you create the table.

Simon|||Ok that simplifies things somewhat. Yes, the columns in question are both
Identity and Primary Key.

Thanks very much for your reply.

Robin

"Simon Hayes" <sql@.hayes.ch> wrote in message
news:41ebea66$1_3@.news.bluewin.ch...
> "Robin Tucker" <idontwanttobespammedanymore@.reallyidont.com> wrote in
> message news:csgov0$4e6$1$830fa17d@.news.demon.co.uk...
>>
>> Can someone explain what happens when two users concurrently attempt to
>> create a new record in a table with an autonumber primary key? For
>> example, user 1 creates a new record and manipulates it within a
>> transaction making use (perhaps) of the @.@.IDENTITY value when creating
>> other, related records. Before this transaction is complete, user 2
>> creates a new record and does the same thing. Presumably they will both
>> have the same @.@.IDENTITY? If this is the case, how is it possible to
>> manage such a situation?
>>
>> Thanks.
>>
> No, each session will have a different value, so there's no problem with
> concurrency - check out SCOPE_IDENTITY(), IDENT_CURRENT() and @.@.IDENTITY
> in Books Online.
> Note that just defining a column as an identity column is not enough to
> guarantee uniqueness - you can still create duplicates manually (see SET
> IDENTITY_INSERT in BOL), so if you want to use the column as a PK, make
> sure it is declared as a PK when you create the table.
> Simon