##index.php
<?php

$ninja = mysql_real_escape_string($ninja); // protect from sql injection.

require_once 'store_ninja.php'; // pretend this is a tough enough task that we'd put it in its own file

//Do other things, make pretty poniz.

?>


##store_ninja.php

<?php

$query = "insert into table_ninjas (name) values '" . $ninja . "';";

mysql_query($query);
?>