Quiz

After a bit of Googling, I found that the code has to do with newer versions of mySQL throwing this error on older versions of Moodle.

The fix was changing /mod/quiz/report/overview/report.php as follows (note the two casts as signed):

Before:
            $select .= 'qa.uniqueid AS attemptuniqueid, qa.id AS attempt, ' .
                    'u.id AS userid, u.idnumber, u.firstname, u.lastname, u.picture, u.imagealt, ' .
                    'qa.sumgrades, qa.timefinish, qa.timestart, qa.timefinish - qa.timestart AS duration ';

After:
            $select .= 'qa.uniqueid AS attemptuniqueid, qa.id AS attempt, ' .
                    'u.id AS userid, u.idnumber, u.firstname, u.lastname, u.picture, u.imagealt, ' .
                    'qa.sumgrades, qa.timefinish, qa.timestart, CAST(qa.timefinish AS SIGNED) - CAST(qa.timestart AS SIGNED) AS duration ';

Just in case someone else runs into the same issue.