PDO: When to use bindParam, execute(array)) and PDO::FETCH_ASSOC? - php

Question

I'm new to PDO, in fact, this is the first time that I'm using it. All the while I've been using mysql which is depreciated. And so recently, I'm trying to update all my site to use PDO which is better and safer according to many sources that I found from the internet.
However, those tutorials is making me even more curious and full of questions. I've been google for the whole day and I still can't get the best answer or examples.
Let's start by this code below,
// query
$sql = "SELECT title FROM books ORDER BY title";
$q = $conn->query($sql);
$q->setFetchMode(PDO::FETCH_ASSOC);
// fetch
while($r = $q->fetch()){
print_r($r);
}
I do understand that it fetches the data just like mysql_fetch_assoc. But, here's another code that I found from the net.
$stmt = $pdo->prepare('SELECT * FROM employees WHERE name = :name');
$stmt->execute(array('name' => $name));
foreach ($stmt as $row) {
// do something with $row
}
and lastly, this:
$stm = $pdo->prepare('SELECT * FROM table LIMIT ?, ?');
$stm->bindParam(1, $limit_from,PDO::PARAM_INT);
$stm->bindParam(2, $per_page,PDO::PARAM_INT);
$stm->execute();
$data = $stm->fetchAll();
Why are there so many different methods to fetch a data ?
I somehow found out that with bindParam, you're able to set integer or strings for the variable? But with this below...
$pdo->execute(array(':col2' => $col2, ':col3' => $col3, ':col4' => $col4));
Am I still able to mix integer and strings without declaring if it's integer or strings?
Is it ok if I do like this ? mixing strings and integer in execute array...
$sql = "INSERT INTO books (id,author) VALUES (:id,:author)";
$q = $conn->prepare($sql);
$q->execute(array(':author'=>'string', ':id'=>1));
And also, does all codes above avoid SQL injection ?
I somehow prefer the execute array method as it is shorter and I don't want to declare if it's integer or strings every time like using the bindParam method.