Including a database connection from a separate file - php

Question

I currently have a db file I include to establish a DB connection:
db.php:
$dbs = array(
"127.0.0.1",
"127.0.0.3",
"127.0.0.2",
);
if(!$con){
$con = mysql_connect($dbs[rand(0,2)],"user_login","password") or die('Could not connect: ' . mysql_error());
}
However when I try to include it sometimes and do a query, it returns a blank result:
include("db.php");
mysql_select_db("database_table", $con);
$result = mysql_query("SELECT * FROM users where email='admin#test.com'");
while($row = mysql_fetch_array($result)){$id = $row['email'];break;}
The weird thing is, if I modify the initial db.php to connect like this, it works (non randomizing it):
db.php:
if(!$con){
$con = mysql_connect("127.0.0.1","user_login","password") or die('Could not connect: ' . mysql_error());
}
Is there any explanation in this? Is there a difference in how they are connecting?
Thanks

Answer 1

First I would turn on error checking.
You can do that by adding the following to the very top of your php file:
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);
or the long way by changing it globally: display_errors = On in your php.ini
This will output what's wrong. If you can't figure it out be then try the following:
Then check if you could connect to all databases like you did with
if(!$con){
$con = mysql_connect("127.0.0.1","user_login","password") or die('Could not connect: ' . mysql_error());
}
Then I would check if they all had the same tables.
If that's correct I would check the output of your:
if(!$con){
$con = mysql_connect($dbs[rand(0,2)],"user_login","password") or die('Could not connect: ' . mysql_error());
}
Does it really work the way it's intended?