Change code to link mySQL into a function - php

Question

I'm new to php. I have this piece of code:
<?php
if (!isset($_GET['id'])) {
die("missing query parameter");
}
$id = intval($_GET['id']);
if ($id === '') {
die("Invalid query parameter");
}
$db = mysql_connect("localhost", "root", "usbw");
$sdb = mysql_select_db("test", $db);
$sql = "SELECT * FROM config WHERE id=$id";
$mq = mysql_query($sql) or die("not working query");
$row = mysql_fetch_array($mq);
?>
And from this code, I want to make a function, but how?
What I'm trying to do is linking my MySQL database to my PHP code, and I also try to use the GET[id] to auto change my page if a change my id.
This piece of code does work, but I want to change it into a function. But I don't know how to start.

Answer 1

Here's an example of a function around your query, mind you it's just an example, as there are many improvements to make.
Such as not using the mysql_* api and moving towards PDO or mysqli_*
But it should be enough to get you started
<?php
// your if logic stays unchanged
$db=mysql_connect("localhost","root","usbw");
$sdb=mysql_select_db("test",$db);
function getConfig($id,$db){
$sql="SELECT * FROM config WHERE id=$id";
$mq=mysql_query($sql);
if ($mq) {
return mysql_fetch_array($mq);
}
else {
return false;
}
}
$results = getConfig($id,$db);
if ($results==false) {
print "the query failed";
}
else var_dump($results);

Answer 2

You can make a file named db.php including some common db functions so you will be able to use them easier:
<?php
function db_connection() {
//SERVER, USER, MY_PASSWORD, MY_DATABASE are constants
$connection = mysqli_connect(SERVER, USER, MY_PASSWORD, MY_DATABASE);
mysqli_set_charset($connection, 'utf8');
if (!$connection) {
die("Database connection failed: " . mysqli_error());
}
return $connection;
}
function db_selection() {
$db_select = mysqli_select_db(MY_DATABASE, db_connection());
if (!$db_select) {
die("Database selection failed: " . mysqli_error());
}
return $db_select;
}
function confirm_query($connection, $result_set) {
if (!$result_set) {
die("Database error: " . mysqli_error($connection));
}
}
function q($connection, $query) {
$result = mysqli_query($connection, $query);
confirm_query($connection, $result);
return $result;
}
?>
Then, you can have your code in some other files:
<?php
require_once('db.php'); //This file is required
$id = $_GET['id']; //Shorthand the $_GET['id'] variable
if (!isset($id)) {
die("missing query parameter");
}
if ( filter_var($id, FILTER_VALIDATE_INT) === false) ) {
die("Invalid query parameter");
}
$sql = "SELECT * FROM config WHERE id = '$id'";
$result = q($connection, $sql);
while ($row = mysqli_fetch_array($result)) {
//Do something
}
?>
Try not to use mysql_* functions because they are deprecated. Use mysqli_* or even better try to learn about prepared statements or PDO.