Simplest example to demonstrate the idea of SQL Injection

index.php

<?php
?>
<h3>Sample login system</h3>
Input <b>admin' OR 1#</b> to in the username field to perform sql injection 
<form method = "POST" action = "landing.php">
  <label for="username">Username:</label><br>
  <input type="text" id="username" name="username"><br>
  <label for="password">Password:</label><br>
  <input type="password" id="password" name="password">
  <input type="submit">
</form>
<?php

landing.php

<?php
$servername = "localhost";
$username = "sql_user_eg_root";
$password = "password_for_sql_user";
$dbname = "sqlinject";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
  die("Connection failed: " . $conn->connect_error);
}


// $user = 'admin';
// $sql = "SELECT username FROM users";

$user = $_POST["username"];
$sql = "SELECT * FROM users WHERE `username` = '$user'";

// echo $sql."<br>";

$result = $conn->query($sql);

if ($result->num_rows > 0) {
  // output data of each row
  echo "<H2>Username found in database</H2>";
  while($row = $result->fetch_assoc()) {
    echo "Username: <b>" . $row["username"]. "</b> lives in <b>".$row["hometown"]."</b> and your password is <b>".$row["password"]."</b><br>";
  }
} else {
  echo "User Not Authorized";
}
$conn->close();
?>