PHP PDO::FETCH_ASSOC Issue - php

Question

My code works but it only works for the first row. When I insert another row in MySQL and try and log-in with the different username and password it returns my error. What's wrong?
<?php
include_once('db.php');
$username = $_POST['username'];
$password = sha1($_POST['password']);
if(!empty($username) && !empty($password)) {
$loginSQL = "SELECT * FROM `users` WHERE `username` = '$username' AND `password` = '$password'";
if($db->query($loginSQL)->fetchColumn() == 1) {
$fetchUsers = $db->query($loginSQL)->fetch(PDO::FETCH_ASSOC);
$userID = $fetchUsers['uid'];
$_SESSION['uid'] = $userID;
echo '<br /><br />You have successfully logged in. Click here to proceed.';
}
else {
echo '<br /><br />You have entered invalid log-in information.';
}
}
else {
echo '<br /><br />You have entered invalid log-in information.';
}
?>

Answer 1

Two biggest problems are double fetch and lack of prepared statements.
<?php
include_once('db.php');
if(!empty($_POST['username'])) {
$username = $_POST['username'];
$password = sha1($_POST['password']);
$sql = "SELECT uid FROM `users` WHERE `username` = ? AND `password` = ?";
$stm = $db->prepare($sql);
$stm->execute(array($username,$password);
if($row = $stm->fetch()) {
$_SESSION['uid'] = $row['uid'];
}
}

Answer 2

There are a few problems here.
fetchColumn() returns the first column of the first row, which might or might not be 1 depending on how the DB table is set up.
fetch() returns the current row the PDOStatement row pointer is on. If you don't send it to the next row, it won't move.
You are sending the same error for two different reason, helping to lead to confusion.
What would really help you is if you would restructure your code like #Your Common Sense shows and look at it then. It will help yourself better see the problem.