[s4shk4]

Разобрался. Вот.

if ololo='' then QueryQuestion.SQL.Text := 'SELECT * FROM Questions WHERE id='+IntToStr(rn)+';'
else
QueryQuestion.SQL.Text := 'SELECT * FROM Questions WHERE ID NOT IN ('+ololo+') ORDER BY RND(id);';

QueryQuestion.Active := true;

if ololo<>'' then ololo := ololo + ',';
ololo := ololo + QueryQuestion.FieldByName('ID').AsString;