按成绩排序并选取前7名科目：PHP与SQL实践教程

SELECT * FROM tbl_student_primary_subject
INNER JOIN tbl_primary_subject ON tbl_primary_subject.subject_id = tbl_student_primary_subject.subject_id
WHERE tbl_student_primary_subject.student_id='$sudentid'
ORDER BY tbl_student_primary_subject.marks DESC;

<?php
// 假设 $con 是数据库连接对象
$sudentid = $_GET['student_id']; // 获取学生ID，请确保进行适当的输入验证和安全处理

$tbl_student_subject_query = "SELECT * FROM tbl_student_primary_subject
    INNER JOIN tbl_primary_subject ON tbl_primary_subject.subject_id = tbl_student_primary_subject.subject_id
    WHERE tbl_student_primary_subject.student_id='$sudentid'
    ORDER BY tbl_student_primary_subject.marks DESC";

$results = $con->query($tbl_student_subject_query);

if ($results) {
    $subjects_results = [];
    $total_marks = 0;
    $count = 0; // 计数器，用于限制只选取前7个科目

    while ($row = $results->fetch_assoc()) {
        if ($count >= 7) {
            break; // 已经选取了7个科目，退出循环
        }

        $subject_marks = $row['marks'];
        $total_marks += $subject_marks;
        $avg_marks = $total_marks / ($count + 1); // 更新平均分计算

        $subjects_results[] = [
            'subject_name' => $row['subject_name'],
            'subject_code' => $row['subject_code'],
            'subject_marks' => $subject_marks,
        ];

        $count++;
    }

    // 现在 $subjects_results 包含了按成绩排序的前7个科目信息
    // 你可以根据需要对 $subjects_results 进行进一步处理或展示
    foreach ($subjects_results as $res) {
        $t = $res['subject_marks'];
        echo "<td>";
        if($t>=75){
            echo $res['subject_marks']." - A";
        }else if($t>=65){
            echo $res['subject_marks']." - B";
        }else if($t>=45){
            echo $res['subject_marks']." - C";
        }else if($t>=30){
            echo $res['subject_marks']." - D";
        }else if($t>0){
            echo $res['subject_marks']." - F";
        }else if($t<0){
            echo "";
        }
        echo "</td>";
    }
} else {
    echo "查询失败: " . $con->error;
}

?>