I want that one person cannot nominate any person twice (only one time allowed). what flag we have to set in the database to avoid the duplicate nomination.

I am using Lime survey Version 2.67.3+170728

Do not double-post. It will not get you an answer any faster.

Can you explain how this relates to LimeSurvey?

Hi ,
I create a survey that have one question type is dropdown which have multiple entries and that entries is same as participants entries (participants who participate in the survey) . I set userleft = 2 in lime_token table , so each participants can fill the survey maximum 2 times . Now , let X be a participants that choose Y 1st time from the drop down during filling the survey 1st time and again if X want to choose Y it should not be allowed for the 2nd time (2nd time means duplicate entries ) . I do not want the duplicate entries .

This is not possible because you have no connectin between the two surveys filled by the same person. It is as if was 2 different people.