how can i do this constrain

[grad2009]

hello guys,
i have a form that is called items, and it contains a field that is called itemNo and the type of this field is number. i want to do my own constraint which prevents the user to enter a number that is previously existed.
i need your help please
many thanks to you,
bye

 

[Rabbie]

hello guys,
i have a form that is called items, and it contains a field that is called itemNo and the type of this field is number. i want to do my own constraint which prevents the user to enter a number that is previously existed.
i need your help please
many thanks to you,
bye

Either generate the number yourself or index it with no duplicates allowed

 

[grad2009]

first, thank you Rabbie for your reply

Either generate the number yourself or index it with no duplicates allowed

I generate the number myself.
thanks with regards,

 

[Rabbie]

If you are generating the number then why are you worried about the users entering a duplicate???

 

[grad2009]

If you are generating the number then why are you worried about the users entering a duplicate???

i'm sorry Rabbie, maybe i didn't understand what you mean, what i mean that i enter the number manually ,not automatically, anyway i found a solution for my problem, i used the dlookup function in the beforeupdate event of the field itemNo
thanks,
regards