Insert data in database File in PHP

 <?php

include("dbconn.php");

if (isset($_POST["add_students"])) {

    $fname = $_POST["f_name"];

    $lname = $_POST["l_name"];

    $age = $_POST["age"];

    if ($fname == "" || empty($fname)) {

        header("location:index.php?message=YOU NEED TO FILL IN THE FIRST NAME");

    } else {

        $sql = "INSERT INTO students(first_name, last_name, age) VALUES('$fname', '$lname', '$age')";

        if ($conn->query($sql) === TRUE) {

            header("location:index.php?insert_msg=YOUR DATA HAS BEEN ADDED SUCCESSFULLY");

        } else {

            die("Query Failed  : " . $conn->error) . "<br>";

            echo "Error : " . $sql . "<br>" . $conn->error;

        }

        $conn->close();

    }

}