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Your LimeSurvey version: Versão 3.18.0+190923
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Hello,

Each time a user interacts with a form the system gets a sequenced id, is it possible to get that sequence only for the completed ones (only when the user clicks on "Submit")?
If the user access to the form, interacted with some questions but didn't complete it, I get a number id for that. Let's say the first three users are in this scenario and the fourth fill-up the form until the last question and effectively submit it, he'll get the number 4, when it should get the number 1.

How can I get to a solution for this?

Thank you

This is not possible, the ID must be created when the first page is submitted because a response row must be created in the database table.

With 5.X : maybe an idea : adding an expression question at the last group with {sum(statCount("id"),1)}