Fatal error: Uncaught mysqli_sql_exception: Expression #1 of ORDER BY clause is not in SELECT list, references column 'allwin-school.exam_schedules.id' which is not in SELECT list; this is incompatible with DISTINCT in /var/www/html/exam-schedule.php:70 Stack trace: #0 /var/www/html/exam-schedule.php(70): mysqli->query('SELECT DISTINCT...') #1 {main} thrown in /var/www/html/exam-schedule.php on line 70