Reusing variables when working with PDO - php

Question

I have to pull data from at least 3 databases, is there anything wrong with reusing my PDO objects?
$dbh = new PDO('mysql:host=' . $host . ';dbname=' . $db_name, $user, $password);
$sth = $dbh->prepare($query1);
// do something
$dbh = new PDO('mysql:host=' . $host2 . ';dbname=' . $db_name2, $user2, $password2);
$sth = $dbh->prepare($query2);
//do something else
Sorry for the edit but here's another consideration. With each of these I obviously should check whether or not the connection was successful and throw an exception if it wasn't:
if (!$dbh) {
$err=$dbh->errorInfo();
throw new Exception('Could not connect: ' . $err[2]);
}
I don't suppose there's a way to avoid this, unless I create all the connections at the same time and do if (!dbh1|!dbh2) { ... }. Just something else to consider.

Answer 1

When you assign $dbh to a new PDO() you are not technically reusing your pdo object. You are creating a new PDO instance and assigning it to a variable that you have previously used. There is nothing wrong with doing this as long as you understand what is occurring in your program.
EDIT:
I'm editing my answer to address the new question you've added to your previous question.
With each of these I obviously should check whether or not the connection was successful and throw an exception if it wasn't:
You can surround your connection attempt in a try catch which is a typical strategy for dealing with connection errors:
<?php
try {
$dbh = new PDO('mysql:host=localhost;dbname=databaseName', $userName, $password);
foreach($dbh->query('SELECT * from TableName') as $row) {
print_r($row);
}
$dbh = null;
} catch (PDOException $ex) {
print "Error!: " . $ex->getMessage() . "<br />";
die();
}
?>

Answer 2

You can do that, but ... don't. Use another variable name (they are cheap) it will make your code much easier to understand. Heck you can (should) even use variable names that will clue you in on what database your object is connecting to, ie:
// connection to data warehouse
$dbh_dataWH = new PDO('mysql:host=' . $host . ';dbname=' . $db_name, $user, $password);
// connection to crm
$dbh_crm = new PDO('mysql:host=' . $host2 . ';dbname=' . $db_name2, $user2, $password2);
This way you will be able to re-use your connection objects, and the code in my very humble opinion will be much clearer for you or anyone else that has to maintain it.