Stop SQL from inserting duplicates (php) - php

Question

It seems to be impossible to do this just with SQL statements, so I wrote a php check, which is completely ignored by the script. $resourse array holds the right data.
public function handleUpdates($updates) {
$stmt = $this->database->connect()->prepare("SELECT ? FROM users"); //<-
$stmt->execute(["username"]); //<-
$resource = $stmt->fetch(PDO::FETCH_ASSOC); //<-
foreach ($updates["result"] as $update) {
$text = $update["message"]["text"];
$args = $update["message"]["chat"]["username"];
if ($text === "/start") {
if ($resource['username'] !== $args) //this here is ignored
$this->database->add($args);
}
}
}

Answer 1

From what I remember about PDO/SQL (I moved to MVC/Doctrine a while back), this part seems a little redundant
$stmt = $this->database->connect()->prepare("SELECT ? FROM users"); //<-
$stmt->execute(["username"]); //<-
and could be replaced with
$stmt = $this->database->connect()->prepare("SELECT username FROM users"); //<-
as you're only ever wanting to get the data found in the username column there's no need to bind it (which isn't fully possible in PDO anyway).
The reason your query fails is that you are using fetch over fetchAll which returns only the first row of results, while this will run it won't give the desired result (which I'm guessing is to check if the username already exists). Even then (as Ivan Vartanyan points out), you would need to foreach or in_array over $resource as it's results are sent as an array anyway.
Realistically you don't need to search and iterate over all the data in PHP, consider searching for your passed username data with SQL instead (code untested);
public function handleUpdates($updates) {
$stmt = $this->database->connect()->prepare("SELECT username FROM users WHERE username = ?");
$stmt->execute(array($update["message"]["chat"]["username"]));
$resource = $stmt->fetch(PDO::FETCH_ASSOC);
if (!$resource) {
foreach ($updates["result"] as $update) {
$text = $update["message"]["text"];
$args = $update["message"]["chat"]["username"];
if ($text === "/start") {
$this->database->add($args);
}
}
}
}