Warning: mysqli_connect(): (HY000/1049): Unknown database code example

Example: php catch mysqli_connect(): (HY000/1045): Access denied

$conn = mysqli_connect( '<server>', '<username>', '<password>',  '<database-name>');
if (!$conn) {
  // whatever processing you want to do upon error in connection
  // like log error or send an email to admin
  // I am just printing the error at the moment.
  echo mysqli_connect_errno() . ":" . mysqli_connect_error();
  exit;
}