php pdo: prepare() vs transactions - php

Question

Are prepare() and transactions mutually exclusive? I've got a lot of queries that I build and then execute, so it sounds like using a transaction is what I want; but I read on the prepare.statment page that using the bindParam method eliminates SQL-injection. Is there some way to do both?
Here's an example of the code I have right now (which may or may not be correct):
$dbhost=FOO;
$dbuser=FOOBAR;
$dbpass=RABOOF;
$options=array(STUFF);
$dbh = new PDO("mysql:host=$dbhost", $dbuser, $dbpass, $options);
// I know this ^ works
$dbh->beginTransaction();
$record_data = $dbh->prepare("UPDATE $db.$tbl SET :column=:value WHERE `key` = :key;");
function record_data($q,$a,$k){
$record_data->bindParam(':column', $q);
$record_data->bindParam(':value', $a);
$record_data->bindParam(':key', $k);
$record_data->execute();
}
// $pairs is an array with ~50 objects/rows
foreach($pairs as $pair){
list($qstn , $ans) = explode('=', $pair);
switch($qstn){
case 1: if(something) record_data($qstn,$ans,$key); break;
case 2: if(something) record_data($qstn,$ans,$key); break;
case 3: if(something) record_data($qstn,$ans,$key); break;
// more
default: record_data($qstn,$ans,$key); break;
}
}
$dbh->commit();
When I tried out the full code, I got No connection could be made because the target machine actively refused it. Usually I see a message like that when my connection info is wrong (or the account isn't set up properly/as I expect). But I tested the PDO connection separately and it worked fine. So I probably did something else wrong.
EDIT: Are variables allowed in prepare()?
EDIT 2: I added try{} around the $dbh = PDO(…) and added echo "connected" at the end of the try (and did the catch bit), and it echo'd "connected", so it is connecting. But after "connected" it prints that error message, so the issue is happening after a successful connection.
EDIT 3: I added
$dbRS = $dbh->query("SELECT * FROM `database`.`table`;");
$row = empty($dbRS) ? false : $dbRS->fetch(PDO::FETCH_ASSOC);
print_r($row);
and it printed the first row of the table, so for sure it's connecting.

Answer 1

"Are mutually exclusive?": No, as you show, is a kind of "function declaration", and transaction is like a (OS) process where the function runs.
"Are variables allowed?": I think you must start checking your PHP function record_data($q,$a,$k): there are a error. Try add global $record_data; at the begin of the function.
General comments: the main advantage of PDO is to capture errors (by PHP error line or returning SQL error messages) for each single SQL statment.
See pdo.begintransaction, pdo.commit, pdo.rollback and pdo.error-handling.
Example:
$dbh->beginTransaction();
/* Do SQL */
$sth1 = $dbh->exec("CREATE TABLE xyz (..)");
$sth2 = record_data($qstn1,$ans1,$key1);
$sth2 = record_data($qstn2,$ans2,$key2);
/* Commit the changes */
$dbh->commit();

Answer 2

You are using vars that were not defined in the scope of the function. Simply use:
global $record_data;
as the first line in the function and it will work.