Update a field value on form submission

Visforms 5.6.3
Joomla 5.4.8
PHP 8.4.24

I have a field "Tally Number" which is currently generated via a SQL query and incremented by one for each time a completed form is submitted. Thus generating a unique sequential number for each form submission starting at 1. All works well until multiple forms are simultaneously opened by different users. This is because the tally number is calculated when the form is opened, but only incremented when the form is submitted. Thus forms opened at the same time get the same Tally Number. Not being a programmer my question is two fold. Can a field be made to calculate only on submission? Or, maybe there is a better way to achieve what I need?
And just for the record VisForms has been simply fantastic for us over many years now in helping us to run our annual sailing event.
Thank you. Nick

Hi Nick,

We are happy to hear, that Visforms works fantastically for your!

There is a field configuration option 'Unique Values Only'.
Field Configuration >> Baisc Settings >> Validation Settings

This option enforce that within records submitted for a form, each user input in this field is unique.
The validation is performed on the server site, directly when the record is stored in the data base.
If there already exists a record with the same value, the form will be redisplayed to the user who came second.

This feature prevents dublicate tally numbers.
You might want to add a usefull php validation error message.
Field Configuration >> General Settings >>'Help-text and Error Messages >> Custom error message (php)

Kind Regards and good luck with your sailing event,
Aicha