What are the best practices for setting up a PHP enrollment system for courses with limited capacity?

When setting up a PHP enrollment system for courses with limited capacity, it is important to implement a check to ensure that the maximum capacity has not been reached before allowing a user to enroll in the course. This can be done by querying the current enrollment count for the course and comparing it to the maximum capacity. If the maximum capacity has been reached, the user should be notified that the course is full and unable to enroll.

// Query the current enrollment count for the course
$current_enrollment_count = // Query database for current enrollment count;

// Check if the current enrollment count is less than the maximum capacity
if($current_enrollment_count < $max_capacity) {
    // Allow user to enroll in the course
    // Insert enrollment data into database
} else {
    // Notify user that the course is full and unable to enroll
    echo "Sorry, this course is currently full and unable to enroll.";
}