using an empty array as a parameter for execute - php

Question

I was reader about PDO , and I was wondering what is the deference between those two methods:
public function query($sql)
{
$req = $this->db->prepare($sql);
$req->execute();
return $req->fetchAll(PDO::FETCH_OBJ);
}
public function query($sql, $data = array())
{
$req = $this->db->prepare($sql);
$req->execute($data);
return $req->fetchAll(PDO::FETCH_OBJ);
}
In the second method, execute has an empty array as a parameter and the first one doesn't, what is the role of using an empty array as a parameter for execute ?

Answer 1

The array is only empty by default. You can pass values in that array and they will be inserted into your SQL statement appropriately (ie - array key=>field name).
Defining an empty array in the function parameters states that this is an optional parameter and you are not forced to pass it - only when it is relevant. For example, when performing an INSERT command. If you don't pass any value to the $data parameter, it's default value will simply be an empty array.
An example of using default parameters -
function saySomething($text="Hello World!"){
echo $text;
}
saySomething(); // will echo out the default "Hello World!"
saySomething("Goodbye World!"); // will echo out "Goodbye World!" as specified.

Answer 2

First one lets you to run a query without parameters.
Second one lets you to run a query either with parameters or without:
$data = $db->query("SELECT * FROM table");
$data = $db->query("SELECT * FROM table WHERE id=?",array($id));
both works.

Answer 3

You can add you parameter bindings in an array instead of using the bindParam() function beforehand.
for instance you wanna select something by id
$stmt = $dbh->prepare("SELECT * FROM `something` WHERE `id` = ?");
$stmt->execute(array($id));
is the same as
$stmt = $dbh->prepare("SELECT * FROM `something` WHERE `id` = ?");
$stmt->bindParam(1, $id, PDO::PARAM_INT, 11);
$stmt->execute();
Though for the bindParam function you can check better,
Check PHP Manual PDO::excute()