Checking entry in a table with PHP PDO issue

I would like to test whether an entry of a particular UID and MID exists in the table user_saved, so here's what I did

$result = $db->prepare("SELECT * FROM user_saved WHERE UID = ? AND MID = ?");   
          $result->execute(array($_SESSION['uid'], $itemId['M开发者_如何学GoID2']));
          $test = $result->fetch(PDO::FETCH_ASSOC); 
                if (isset($test)){
        exist
      } else {
                    doesn't exist
              }

The issue is that I tried with a UID and MID that doesn't exist, but it always goes into the isset if statement, why is this? What's a better way to do this?

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isset checking whether variable exists or not use strlen function or array count function

<?php
$bbnq = sprintf("SELECT login
FROM users
WHERE id = %u",27);
try
    { $req = $db_bbn->query($bbnq); }
catch (Exception $e)
    { bbnf_pdo_error($e,__FILE__,__LINE__); }
if ( $r = $req->fetch() )
    { echo "This query has a row result"; }
else
    { echo "This query has an empty result"; }
?>

---

fetch returns FALSE on failure:

if ($test !== FALSE) // ...