Explanation of Fetch_semesters

Code Breakdown

1. Database Connection

require 'db_connection.php';

• This line includes the db_connection.php file, which establishes the database connection using the $conn variable.
• Without this file, the script won't be able to query the database.

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2. Fetching the Course ID

$course_id = $_GET['course_id'];

• Retrieves the course_id from the URL using the $_GET superglobal.
• The course_id is used to filter semesters based on the selected course.

Example:
If the URL is script.php?course_id=5, $course_id will contain the value 5.

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3. SQL Query

$query = "SELECT id, name FROM semesters WHERE course_id = $course_id";

• A SELECT query retrieves the id and name columns from the semesters table, filtering rows where course_id matches the provided value.

Example Query for course_id = 5:

SELECT id, name FROM semesters WHERE course_id = 5;

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4. Executing the Query

$result = $conn->query($query);

• The query is executed using the $conn->query() method.
• The result is stored in the $result variable.

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5. Checking Results

if ($result->num_rows > 0) {

• Checks if the query returned any rows.
• num_rows: Indicates the number of rows in the result set.

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6. Generating Dropdown Options

·         Default Option:

echo '<option value="">Select Semester</option>';

• Adds a default option prompting the user to select a semester.

·         Iterating Through Rows:

while ($row = $result->fetch_assoc()) {

    echo "<option value='{$row['id']}'>{$row['name']}</option>";

}

• fetch_assoc() fetches each row as an associative array.
• For each row:
• The id is set as the value attribute of the <option> tag.
• The name is displayed as the visible text in the dropdown.

Example Output for Semesters:

<option value="">Select Semester</option>

<option value="1">Semester 1</option>

<option value="2">Semester 2</option>

<option value="3">Semester 3</option>

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7. Handling No Results

{

    echo '<option value="">No Semesters Available</option>';

}

• If the query returns zero rows, an <option> is added to inform the user that no semesters are available.

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Expected Usage

This script is often used to populate a semester dropdown in a cascading dropdown system.
Example Workflow:

1.A user selects a course in a dropdown menu.

2.Using JavaScript (e.g., AJAX), the course_id is sent to this script via a GET request.

3.The script generates a list of semesters for the selected course, which is dynamically displayed in the semester dropdown.

Example Dropdown:

<select name="semester" id="semester-dropdown">

    <?php include 'generate_semesters.php?course_id=5'; ?>

</select>

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Key Features

1.Dynamic Data Loading:

o    Dropdown options are dynamically generated based on the selected course.

2.Database Integration:

o    Fetches semesters from the database, ensuring up-to-date data.

3.Empty State Handling:

o    Displays an appropriate message if no semesters are available.

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Potential Improvements

1.Validation and Error Handling:

o    Validate course_id to ensure it’s a valid integer.

if (!is_numeric($course_id)) {

    die('Invalid Course ID');

}

o    Check if the query execution was successful.

if (!$result) {

    die("Query failed: " . $conn->error);

}

2.SQL Injection Prevention:

o    Use prepared statements to secure the query.

Example:

$stmt = $conn->prepare("SELECT id, name FROM semesters WHERE course_id = ?");

$stmt->bind_param("i", $course_id); // 'i' indicates integer

$stmt->execute();

$result = $stmt->get_result();

3.Output Sanitization:

o    Escape special characters to prevent XSS attacks.

echo "<option value='" . htmlspecialchars($row['id']) . "'>" . htmlspecialchars($row['name']) . "</option>";

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How It Works

When included in a form, the script dynamically generates <option> elements for semesters based on the course selected by the user.

Example Scenario:

• A user selects "Computer Science" (course ID: 5).
• The script runs with ?course_id=5.
• The dropdown is populated with semesters available for "Computer Science."

This approach ensures the dropdown options are always in sync with the database.