There are two ways to connect to a MySQL/MariaDB server, depending on your infrastructure.

Standard (TCP/IP) connection

$dsn = 'mysql:dbname=demo;host=server;port=3306;charset=utf8';
$connection = new \PDO($dsn, $username, $password);

// throw exceptions, when SQL error is caused
$connection->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
// prevent emulation of prepared statements
$connection->setAttribute(\PDO::ATTR_EMULATE_PREPARES, false);

Since PDO was designed to be compatible with older MySQL server versions (which did not have support for prepared statements), you have to explicitly disable the emulation. Otherwise, you will lose the added injection prevention benefits, that are usually granted by using prepared statements.

Another design compromise, that you have to keep in mind, is the default error handling behavior. If not otherwise configured, PDO will not show any indications of SQL errors.

It is strongly recommended setting it to “exception mode”, because that gains you additional functionality, when writing persistence abstractions (for example: having an exception, when violating UNIQUE constraint).

Socket connection

$dsn = 'mysql:unix_socket=/tmp/mysql.sock;dbname=demo;charset=utf8';
$connection = new \PDO($dsn, $username, $password);

// throw exceptions, when SQL error is caused
$connection->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
// prevent emulation of prepared statements
$connection->setAttribute(\PDO::ATTR_EMULATE_PREPARES, false);

On unix-like systems, if host name is 'localhost', then the connection to the server is made through a domain socket.