I found this line at 303 - 305
$select = 'SELECT '.sql_concat('u.id', '\'#\'',$db->IfNull('qa.attempt', '0')).' AS uniqueid, '. 'qa.uniqueid as attemptuniqueid, qa.id AS attempt, u.id AS userid, u.firstname, u.lastname, u.picture, '. 'qa.sumgrades, qa.timefinish, qa.timestart, qa.timefinish - qa.timestart AS duration ';
But after I replace 'u.firstname, u.lastname' with u.username, the output became Empty.
Can anyone help? I needed the username because it cannot be changed (student id)