Sort by results and select the top 7 subjects: PHP and SQL practical tutorials

This tutorial is designed to help developers use PHP and SQL to sort student subject scores and select the 7 subjects with the highest scores. We will modify the SQL query statement, use the ORDER BY clause to sort by grades in descending order, and perform data processing in the PHP code to finally extract the required subject information. This tutorial will provide detailed SQL statements and PHP code examples, as well as precautions to ensure readers can understand and successfully apply them.

In the student performance management system, it is often necessary to sort students according to their subject scores and select the top-ranked subjects for display or analysis. This article will introduce how to use PHP and SQL to implement this function, focusing on the optimization of SQL queries and data processing of PHP code.

SQL query: Sorting using ORDER BY

SQL's ORDER BY clause allows us to sort query results by one or more columns. By default, ORDER BY sorts in ascending order (ASC). If you need to sort in descending order, you need to use the DESC keyword.

In your scenario, you need to sort in descending order according to subject_marks (subject scores). Therefore, the SQL query statement needs to be modified as follows:

 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;

explain:

• ORDER BY tbl_student_primary_subject.marks DESC: This part of the code instructs the database to sort in descending order according to the marks field in the tbl_student_primary_subject table. Make sure to use the correct table and field names.

PHP code: Process the query results and select the top 7

The modified SQL query will return all subjects in descending order of grades. Next, you need to process the query results in PHP code and select the top 7 subjects.

 <?php // Assume $con is the database connection object $sudentid = $_GET[&#39;student_id&#39;]; // Get the student ID, please ensure proper input validation and security processing $tbl_student_subject_query = "SELECT * FROM tbl_student_primary_subject
    INNER JOIN tbl_primary_subject ON tbl_primary_subject.subject_id = tbl_student_primary_subject.subject_id
    WHERE tbl_student_primary_subject.student_id=&#39;$sudentid&#39;
    ORDER BY tbl_student_primary_subject.marks DESC";

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

if ($results) {
    $subjects_results = [];
    $total_marks = 0;
    $count = 0; // Counter, used to limit the selection of only the first 7 accounts while ($row = $results->fetch_assoc()) {
        if ($count >= 7) {
            break; // 7 subjects have been selected, exit the loop}

        $subject_marks = $row['marks'];
        $total_marks = $subject_marks;
        $avg_marks = $total_marks / ($count 1); // Update average score calculation $subjects_results[] = [
            'subject_name' => $row['subject_name'],
            'subject_code' => $row['subject_code'],
            'subject_marks' => $subject_marks,
        ];

        $count ;
    }

    // Now $subjects_results contains the first 7 subject information sorted by grades // You can further process or display $subjects_results as needed foreach ($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";
    }
} else {
    echo "Query failed: " . $con->error;
}

?><p> <strong>explain:</strong></p>
<ol>
<li> <strong>SQL query execution:</strong> Execute the modified SQL query and obtain the sorted result set.</li>
<li> <strong>Loop through the results:</strong> Use a while loop to traverse the result set, and use the fetch_assoc() function to obtain each row of data as an associative array.</li>
<li> <strong>Counter:</strong> Use the $count variable as a counter to record the number of accounts that have been selected.</li>
<li> <strong>Limit the number of selections:</strong> Inside the loop, determine whether $count reaches 7. If it reaches 7, use the break statement to exit the loop, ensuring that only the first 7 subjects are selected.</li>
<li> <strong>Data processing:</strong> Store the relevant information of each subject (subject name, subject code, subject results) into the $subjects_results array.</li>
<li> <strong>Output results:</strong> Finally, traverse the $subjects_results array and output the grade level of each subject.</li>
</ol>
<p> <strong>Things to note:</strong></p>
<ul>
<li> <strong>SQL Injection:</strong> Be sure to perform proper input validation and escaping of $sudentid to prevent SQL injection attacks. You can use Prepared Statements to handle user input more safely.</li>
<li> <strong>Error handling:</strong> Add appropriate error handling mechanisms, such as checking whether the database connection is successful, whether the query is executed successfully, etc.</li>
<li> <strong>Performance optimization:</strong> If the amount of data is very large, you can consider using indexes to optimize query performance.</li>
</ul>
<h3> Summarize</h3>
<p> By modifying the SQL query statement, using the ORDER BY clause to sort in descending order by grades, and adding counters and conditional judgments in the PHP code, you can easily implement the function of sorting by grades and selecting the top 7 subjects. Remember, security, error handling, and performance optimization are important areas to focus on during development.</p>
</td>

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