To connect to the database, it is convenient to create a separate file in which to enter the parameters for connection. Let’s create this file and name it connection.php
Next add some content to connection.php file:
//сreate variables in which parameters for connection are entered
$host = 'localhost';
$db = 'my_db';
$user = 'root';
$pass = 'root';
$charset = 'utf8';
//from our variables we will form request for PDO connection
$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
$options = [
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,//set options for PDO connection
PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,//Sets the default sampling mode
];
//make a PDO connection
$pdo = new PDO($dsn, $user, $pass, $options);
PDO functions
$res = $pdo->prepare("SELECT COUNT(*) FROM users WHERE login = ?");//prepares a query for execution and returns the object associated with the query
$res->execute([$login]);//runs a prepared query for execution
$res->fetchColumn();//returns data from one column of the next row in the resulting table. If there are no more rows as a result of the query, the function will return false.
$res->fetch();//retrieves the next row from the object's result set
$pdo->query("SELECT * FROM messages");//executes a SQL query in which receives all data from the messages table
$pdo->fetchAll();//convert data to an array of results
Read more about this functions or search a new – https://www.php.net/manual/en/book.pdo.php