包括和MySQL

Question

I need to make one connection to the database and use it everywhere in my PHP files. I understand include but maybe I don't fully. If I make a PHP file with the functions to connect to a database and leave a variable for it, then include that file in 2 PHP files. Will there be 2 connections? How can I just make one single connection and use the variable everywhere?

Also note that I'm going to use PDO, it would be better if you provide help with PDO's syntax.

Answer 1

The database will connect each time a page loads, regardless of how many php files are included in the page load.

So, you can limit the number of connections to one per page load.

In order to do this, you create a connection file, containing something along the lines of:

$user = 'database_username';
$pass = 'a_Hard_Password';
$dbh = new PDO('mysql:host=localhost;dbname=test', $user, $pass);

You will then save that file, naming it something like db.php or similar.

Then, in whichever files you need to use the database, you will include the file one time by utilizing require_once, as follows:

require_once 'db.php';

$results = $db->query('SELECT * FROM my_table');
foreach($results AS $row) {
    var_dump($row);
}

There's plenty of good resources out there, and this is simply an example, but for a more complex query, one of the advantages of PDO is bound parameters, like so:

$id = 5; // Or some other useful value
$name = 'James'; // Or your desired query value
$stmt = $db->prepare("SELECT * FROM my_table WHERE id=? AND name=?");
$stmt->execute(array($id, $name));
$results = $stmt->fetchAll(PDO::FETCH_ASSOC);
foreach($results AS $row) {
    // The PDO::FETCH_ASSOC parameter tells it to return an associative array...
    echo $row['id'];
    echo $row['name'];
   // ... etc ...
}