mysql> SELECT student_id, GROUP_CONCAT(courses_id) AS courses FROM student_courses WHERE student_id=2 GROUP BY student_id; +------------+---------+ | student_id | courses | +------------+---------+ | 2 | 3,4,5 | +------------+---------+ 1 row IN SET (0.00 sec)
$row = $pdo->query("SELECT student_id, GROUP_CONCAT(courses_id) AS courses FROM student_courses WHERE student_id=2 GROUP BY student_id"); $result = explode(',', $row['courses']);