php中的变量作用域

<?php
    include_once $_SERVER[‘DOCUMENT_ROOT‘].‘/includes/db.inc.php‘;
function totalJokes()
{
try{
      $result=$pdo->query(‘SELECT joketext FROM joke‘);//此处的$pdo应该改为$GLOBALS[‘pdo‘]
    
}catch(PDOEXceptio $e){
    $output=‘eror to connect database‘.getMessage();
    include‘output.html‘;
    exit();
}....