How To Avoid Duplicate Record Entry In A Detail Table

Check this article from the manual: http://xlinesoft.com/phprunner/docs/check_if_specific_record_exists.htm

Thanks christian, i didn't mean duplicate record in database, but duplicate entry in add form .

On the screenshot above, my customer made a mistake. He added the same product twice in order form.

I'm not sure I understand your request. A duplicated entry on the add form will be tapped as a duplicated record in the database.

Is that you don't want to have duplicate value in the view showing?

try use mysql 'group by' for the page showing.

This is something like Form Validation in add form.
what I want is : when a customer accidentally enters the same product (which has been added to the previous field) , an alert box will appear .... ""..
screenshot :

As I said in my previous message, check for existing record (http://xlinesoft.com/phprunner/docs/check_if_specific_record_exists.htm) and when you save all, the duplicate record will throw an error.

Cristian is correct, use BeforeAdd event to check for duplicates and display the message.
Another option is to check for duplicates in BeforeAdd and simply ignore the duplicate record.