NFC based attendance system with Arduino Uno, Ethernet Shield and Adafruit PN532

Hi there, we are currently working on a NFC based attendance system using the above mentioned products in the subject matter. We’re using php as our intermediary between arduino and the MySQL database hosted on our localhost. For testing purposes, we have created a php file with a simple insert query.
save.php

<?php
 $servername = "localhost";
 $username = "root";
 $password = "";
 $dbname = "nfcreader";
 
//create variable

 //create connection
 $conn = new mysqli($servername, $username, $password, $dbname);

 //check connection
 if ($conn->connect_error){
	die("Connection failed: " . $conn->connect_error);
 }
 echo "Connected successfully";

 $sql = "INSERT INTO student_attendance (student_id) VALUES ('1475847513')";

 if($conn->query($sql) === TRUE) {
	echo "New record created succesfully";
 } else {
	echo "Error: " . $sql . "
" . $conn->error;
 }
 
 $conn->close(); 
 ?>

Our issue is that while we’re able to read multiple card inputs from the Adafruit PN532 NFC reader, but we’re not able to pass multiple inputs to our database.

readMifareClassic.ino (6.15 KB)

Is your database set up to require unique entries for the student_id column?

Why is every tag scanned considered the same student?