How to stop duplicate entry

dear sir/madam
I have made an project in asp with sql server. All database are
without any primary key.
In one times many people are doing entry. So there is one field for
serial number generation and all value of this field should be unique.
But due to huge amount of entry some times clients entry
simultaneously and duplicate value enters in the field. Please tell me
how to stop it. I just want If record of one person is inserting then
other person record should be in wait so that duplicate entry should
not be entered

Thanks in Advance

There are a number of ways to solve this common problem.
Read up on the identity data type and the @@IDENTITY function. The identity
data type is intended for this purpose.
I know that you may have trouble modifying an existing application to use an
identity value. You can at least add a unique index on that column of the
table to absolutely prevent duplicate values.
--
Rick Byham (MSFT)
This posting is provided "AS IS" with no warranties, and confers no rights.

wrote in message

> dear sir/madam
> I have made an project in asp with sql server. All database are
> without any primary key.
> In one times many people are doing entry. So there is one field for
> serial number generation and all value of this field should be unique.
> But due to huge amount of entry some times clients entry
> simultaneously and duplicate value enters in the field. Please tell me
> how to stop it. I just want If record of one person is inserting then
> other person record should be in wait so that duplicate entry should
> not be entered
>
> Thanks in Advance