PDO Insert value - php

Question

I have followed some tutorial and I can't understand why this doesn't work.
I have a class Users. It gets a DB connection in the __construct method. Next I have a Create method, that needs to create a user by inserting some data in the table, but it does not execute. I think I have problem with the bindParam function or with MySQL insert code.
I have following error:
Warning: PDOStatement::execute(): SQLSTATE[HY093]: Invalid parameter number: parameter was not defined in C:\www\samodel\object\users.php on line 44
Please help me to solve this problem if you know how, Thank you:
<?php
//Was Products, now Users
class Users{
// database connection and table name
private $conn;
private $table_name = "users";
// object properties
public $id;
public $username;
public $first_name;
public $last_name;
public $email;
public $password;
public function __construct($db){
$this->conn = $db;
}
// create user
function create(){
//write query
$query = "INSERT INTO
" . $this->table_name . "
SET
username = ?, first_name = ?, last_name = ?";
$stmt = $this->conn->prepare($query);
$stmt->bindParam("username", $this->username);
$stmt->bindParam("first_name", $this->first_name);
$stmt->bindParam("last_name", $this->last_name);
if($stmt->execute()){
return true;
}else{
return false;
}
}
}
?>

Answer 1

You are mixing two techniques here - you are preparing the statement with positional placeholders, but binding according to names - you should pick one and stick to it.
With positional placeholders:
$query = "INSERT INTO
" . $this->table_name . "
SET
username = ?, first_name = ?, last_name = ?";
$stmt = $this->conn->prepare($query);
$stmt->bindParam(1, $this->username);
$stmt->bindParam(2, $this->first_name);
$stmt->bindParam(3, $this->last_name);
With named placeholders:
$query = "INSERT INTO
" . $this->table_name . "
SET
username = :username, first_name = :first_name, last_name = :last_name";
$stmt->bindParam("username", $this->username);
$stmt->bindParam("first_name", $this->first_name);
$stmt->bindParam("last_name", $this->last_name);

Answer 2

I think you have bad sql
try
$query = "INSERT INTO {$this->table_name} (username, first_name, last_name) VALUES (:username, :first_name, :last_name)";