Get earliest year from multiple tables - php

Question

I have a couple tables where there is a same field added. What I want to do is get the earliest year from all these records.
Tables:
comics | movies | tv | tv_episodes
Code So Far (Doesn't Work):
function getStartYear() {
include("config.php");
$query = "SELECT DATE_FORMAT(added, '%Y') as `added` FROM (comics,movies,tv,tv_episodes) ORDER BY `added` DESC LIMIT 1";
$result = mysql_query($query);
while ($row = mysql_fetch_array($result)) {
return $row['added'];
}
}
Error Returned:
Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in E:\xampp\htdocs\mydb\functions\common.php on line 94
What would be the most efficient way to do this?
UPDATE
So going by Andrew's answer the new query looks like:
function getStartYear() {
include("config.php");
$query = "SELECT MIN(y) FROM (
SELECT MIN(YEAR(added)) AS y FROM comics
UNION SELECT MIN(YEAR(added)) AS y FROM movies
UNION SELECT MIN(YEAR(added)) AS y FROM tv
UNION SELECT MIN(YEAR(added)) AS y FROM tv_episodes
) AS t1";
$result = mysql_query($query);
if (mysql_num_rows($result) > 0) {
$finalanswer = mysql_fetch_array($result);
return $finalanswer['t1']; // <-- Line 96
}else{
echo mysql_error();
}
}
New Message:
Notice: Undefined index: t1 in E:\xampp\htdocs\mydb\functions\common.php on line 96

Answer 1

Could retrieve it through SQL using a UNION sub-query:
SELECT MIN(y) FROM (
SELECT MIN(YEAR(added)) AS y FROM table1
UNION SELECT MIN(YEAR(added)) AS y FROM table2
...
) AS t1;

Answer 2

First you should be checking to make sure your SQL statement actually returns the desired data. Run the script itself in some sort of SQL viewer (or phpMySQL), or
echo mysql_error();
just to be sure you don't have an invalid SQL statement.
The invalid resource error you're getting indicates to me that the "$result" of your mysql_query function is not a valid resource.
So:
if (!$result = mysql_query($query))
echo mysql_error();
if you do have an error in your query, diagnose and fix and go from there...
As it stands right now, you're doing a "return" from the middle of a loop, which means you're returning the first object found in the result set.
I would consider instead of "looping", do this:
if (mysql_num_rows($result) > 0)
{
$finalanswer = mysql_fetch_array($result);
return $finalanswer['added'];
}
else
echo mysql_error();
error trapping is kind of a nice thing to get in the habit of. :)