Convert WordPress MySQL data to .JSON file

Trying to figure out to create a .json file using a PHP script rather than a plugin (which doesn’t really create a JSON file on the server anyway). I’m using the following PHP code and it does create a .json file but with null data. Any idea how to properly do this?

<?php
$con=mysql_connect("hostname","database_user","database_password") or die("Database connection failed");
if($con)
{
mysql_selectdb("database_wp",$con);
}
?>

<?php

$data=array();
$qa=array();
$query=mysql_query("SELECT id, title, content FROM wp_posts ORDER BY id");
while($geteach=mysql_fetch_array($query))
{
$id=$getputnam[0];
$title=$getputnam[1];
$content=$getputnam[2];
$qa[]=array('id'=> $id, 'title'=> $title, 'content'=> $content);
}
$data['qa']=$qa;

$fp = fopen('myjson.json', 'w');
fwrite($fp, json_encode($data));
fclose($fp);

?>