Data not inserted in MySQL database, but there's no error

Question

First of all, I am new to the use of php, XAMPP and SQL. I put a lot of time in trying to solve this problem on my own but nothing I did solved it.

I want to insert data from a input form on my website into my Database. When I fill out the form, the script runs without complaints but no data is inserted into my database. Also no errors shown in myphpadmin, simply 0 rows returned.

<?php

if (isset($_POST['submit'])) {

    include_once 'database.php';

    $first_name = mysqli_real_escape_string($conn, $_POST['first_name']);
    $last_name = mysqli_real_escape_string($conn, $_POST['last_name']);
    $username = mysqli_real_escape_string($conn, $_POST['username']);
    $password = mysqli_real_escape_string($conn, $_POST['password']);
    $pin = mysqli_real_escape_string($conn, $_POST['pin']);

    //Errors
    //Check for NOT NULL
    if (empty($first_name) || empty($last_name) || empty($username) || empty($password))
         {
        header("Location: ../signup.php?signup=empty");
        exit();
    } else {
        //check if input charakters are valid
        if (!preg_match("/^[a-zA-Z]*$/", $first_name) || !preg_match("/^[a-zA-Z]*$/", $last_name)) 
            {
                header("Location: ../signup.php?signup=invalid");
                exit();
            } else {
             $sql = "SELECT * FROM user WHERE username='$username'"; 
             $result = mysqli_query($conn, $sql);
             $resultCheck = mysqli_num_rows($result);

             if ($resultCheck > 0) {
                header("Location: ../signup.php?signup=usertaken");
                exit();
               } else {
                //Hashing Password
                $hashedpassword = password_hash($password, PASSWORD_DEFAULT);
                //insert user into database
                $sql = "INSERT INTO user (first_name, last_name, username, password, pin) VALUES ('$first_name', '$last_name', '$username', '$hashedpassword', '$pin');";
                mysqli_query($conn, $sql);
                header("Location: ../signup.php?signup=success");
                exit();
               }
            }
        }

} else {
    header("location: ../signup.php");
    exit();
}

the database is standard setup with root, localhost and no PW

<?php

$dbServername ="localhost";
$dbUsername ="root";
$dbPassword ="";
$dbName ="ntust";

$conn = mysqli_connect($dbServername, $dbUsername, $dbPassword, $dbName);

?>

As I am also not very familiar with SQL, I start to wonder if the problem lies in my tables?

CREATE TABLE user (
id Bigint(20) Primary Key auto_increment,
username varchar(255) NOT NULL unique,
pin varchar(6) NOT NULL,
password varchar(255) NOT NULL,
first_name varchar(255) NOT NULL,
last_name varchar(255),
last_modified_date datetime NOT NULL,
created_date datetime NOT NULL
);

Answer 1

Database Connection

$dbServername ="localhost";
$dbUsername ="root";
$dbPassword ="";
$dbName ="ntust";

$conn = mysqli_connect($dbServername, $dbUsername, $dbPassword, $dbName);

?>

Database Format

CREATE TABLE user (
id Bigint(20) Primary Key auto_increment,
username varchar(255) NOT NULL unique,
pin varchar(6) NOT NULL,
password varchar(255) NOT NULL,
first_name varchar(255) NOT NULL,
last_name varchar(255),
last_modified_date datetime NOT NULL,
created_date datetime NOT NULL
);

Updated Code

<?php

    if (isset($_POST['submit']) && !empty($_POST['first_name']) && !empty($_POST['last_name']) && !empty($_POST['username']) && !empty($_POST['password']) && !empty($_POST['pin'])) {


        if (!preg_match("/^[a-zA-Z]*$/", $_POST['first_name']) || !preg_match("/^[a-zA-Z]*$/", $_POST['last_name'])) {
            # code...
             header("Location: ../signup.php?signup=empty");
             exit();
        }
        elseif (!preg_match("/^[a-zA-Z]*$/", $_POST['first_name']) || !preg_match("/^[a-zA-Z]*$/", $_POST['first_name'])) {
            # code.. check if input charakters are valid
             header("Location: ../signup.php?signup=invalid");
             exit();
        }


         include_once 'database.php';

         $first_name = $_POST['first_name'];
         $last_name = $_POST['last_name'];
         $username = $_POST['username'];
         $password = $_POST['password'];
         $pin =  $_POST['pin'];
         $last_modified_date = date("d-m-Y");
         $created_date = date("d-m-Y");

         $sql = "SELECT * FROM user WHERE username='$username'"; 
                 $result = mysqli_query($conn, $sql);
                 $resultCheck = mysqli_num_rows($result);

                 if ($resultCheck > 0) {
                    header("Location: ../signup.php?signup=usertaken");
                    exit();
                   } else {
                    //md5 Password
                    $md5password = md5($password);
                    //insert user into database
                   $sql = "INSERT INTO user (first_name, last_name, username, password, pin,last_modified_date,created_date) VALUES ('$first_name', '$last_name', '$username', '$md5password', '$pin','$last_modified_date','$created_date ');";
                    mysqli_query($conn, $sql);
                    header("Location: ../signup.php?signup=success");
                    exit();
             }



    }
    else {

    $error = " Fill the all the details first";

    if (isset($_POST['submit']) && isset($error)) {

        echo "$error";
    }

    }   
?>  

Note: as i checked your database you, have an last_modified_date datetime NOT NULL, and created_date datetime NOT NULL So, Update it Based on this code, other every things is fine !!

Answer 2

Based to your experience I would say that the following the most appropriate solution.

Change your code to:

$result = mysqli_query($conn, $sql); 

if (!$res) {
  printf("Errormessage: %s\n", mysqli_error($conn));
}

In this way you can check if there is an error on your query

I would suggest to start looking for simple code debugging techniques and start searching for the appropriate documentation for php and mysqli

You can always check the mysqli_error() w3schools documentation here