我嘗試制作學(xué)生成績(jī)管理系統(tǒng)。當(dāng)我試圖根據(jù)每個(gè)學(xué)生在考試中獲得的總分來(lái)確定位置時(shí)，我遇到了問(wèn)題。在我的輸出中，我得到 1st（獲得標(biāo)記 450）、2nd（獲得標(biāo)記 449）、4th（獲得標(biāo)記 448）。缺少第 3 個(gè)位置。5、10 和其他一些位置丟失。但是我在我的代碼中沒(méi)有發(fā)現(xiàn)任何問(wèn)題。if (!function_exists('get_position_in_exam')) {function get_position_in_exam($school_id, $exam_id, $class_id, $section_id, $mark) {    $ci = & get_instance();    $sql = "SELECT id, total_obtain_mark, FIND_IN_SET( total_obtain_mark,(            SELECT GROUP_CONCAT( total_obtain_mark  ORDER BY total_obtain_mark DESC )             FROM exam_results WHERE school_id = $school_id AND exam_id = $exam_id AND class_id = $class_id AND section_id = $section_id ))            AS rank             FROM exam_results            WHERE school_id = $school_id AND exam_id = $exam_id AND class_id = $class_id AND section_id = $section_id AND total_obtain_mark = $mark";     $rank =  @$ci->db->query($sql)->row()->rank;     if($mark == 0){        return '--';     }    if($rank == 1){        return $rank.'st';    }elseif($rank == 2){       return $rank.'nd';     }elseif($rank == 3){       return $rank.'rd';     }elseif($rank > 3 ){        return $rank.'th';             }else{        return '--';     }}}