数据无法正确从数据库中获取

Question

我试图建立学生成绩管理系统。当我试图根据每个学生在考试中的总成绩而给每个学生分配职位时，我会遇到问题。在我的输出中，我得到第一（获得标记450），第二（获得标记449），第四（获得标记448）。第三位置丢失。 5、10和其他一些位置也缺少。但是我在代码中没有发现任何问题。

我的数据库

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 '--'; 
    }
}

}

Answer 1

您的子查询中需要不同的total_obtain_mark

GROUP_CONCAT( distinct total_obtain_mark ORDER BY total_obtain_mark DESC )

"SELECT id, total_obtain_mark, FIND_IN_SET( total_obtain_mark,(
   SELECT GROUP_CONCAT( distinct 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";

否则，如果您有一些同等级的学生，则跳过位置