Untitled

<?php
    if(isset($_POST['submit']) && !empty($_POST['query'])){
$query =  $_POST['query'];
 mysql_query($query);

}

    ?>

<form action="" method="post">
    <div>
        <textarea name="query"></textarea>
        <input type="submit" name="submit" value="submit" />
    </div>
</form>

<?php

    /* query.php */
    $query = $_REQUEST['query']; //do SQLi prevention
    $conn  = new mysqli('localhost', 'root', '', 'db');
    if($conn->connect_error) throw new Exception('Failed to connect to MySQL server.'); //have the script handle the exception elsewhere
    if($conn->query($query) !== false)
    {
        echo 'Query executed successfully.';
    }
    $conn->close();

<!DOCTYPE html>
  <!-- index.html -->
  <html>
    <head>
    </head>
    <body>
      <form method='POST' action='query.php'>
        <input type='text' name='query' />
        <br />
        <input type='submit' />
      </form>
    </body>
  </html>