PHP/MySQL/PDO-结果为false，但没有DB错误消息

我有一段代码执行异常。有时有效，有时无效。该服务器有一个绝对古老的PHP副本（5.1.6，已有五年历史，但带有由Red Hat手动后移植的安全补丁）。

这是代码，包括我目前的调试行：

<?php
// Includes json_print, which does a json_encode, an 
// appropriate content-type header, prints it, and exits the script.
include_once('json-functions.php');
$uid = $_POST['uid'];
$salted = false;
if(isset($_POST['salted'])){ $salted = true; }
// No uid given.
if(is_null($uid) || $uid === ''){
        $details = array(
            'error' => 1,
            'errorMessage' => 'No unique ID entered.  Please try again.',
        );
        json_print($details);
}
// Validate uid.  Must be 64 digit hexadecimal value.
$pattern = '/^[a-f0-9]{64}$/i';
if(preg_match($pattern, $uid) === 0){
        $details = array(
            'error' => 2,
            'errorMessage' => 'Invalid unique ID.',
        );
        json_print($details);
}

include_once('../db.php');
header('Content-Type: text/plain');
// Is this salted already?
var_dump($salted);
// What's the UID?
var_dump($uid);
if(!$salted){ $uid = hash('sha256', $salt.$uid); }
// Was the UID salted?  (shouldn't be double-salted)
var_dump($uid);
// The query
$SQL = 'SELECT ';
    $SQL .= 'p.patronID AS patronID, ';
    $SQL .= 'uniqueID, ';
    $SQL .= 'status, ';
    $SQL .= 'active, ';
    $SQL .= 'd.name AS department, ';
    $SQL .= 'docdelivery, ';
    $SQL .= 'terms, ';
    $SQL .= 'copyright, ';
    $SQL .= 'lastLogin, ';
    $SQL .= 'updated, ';
    $SQL .= 'TIMESTAMPDIFF(MINUTE, lastLogin, NOW()) AS recency, ';
    $SQL .= 'DATEDIFF(NOW(), updated) AS stale, ';
    $SQL .= 'AES_DECRYPT(first, ?) AS first, ';
    $SQL .= 'AES_DECRYPT(last, ?) AS last, ';
    $SQL .= 'AES_DECRYPT(barcode, ?) AS barcode, ';
    $SQL .= 'INET_NTOA(AES_DECRYPT(ip, ?)) AS ip, ';
    $SQL .= 'AES_DECRYPT(email, ?) AS email, ';
    $SQL .= 'AES_DECRYPT(phone, ?) AS phone, ';
    $SQL .= 'AES_DECRYPT(address1, ?) AS address1, ';
    $SQL .= 'AES_DECRYPT(address2, ?) AS address2, ';
    $SQL .= 'AES_DECRYPT(city, ?) AS city, ';
    $SQL .= 'AES_DECRYPT(state, ?) AS state, ';
    $SQL .= 'AES_DECRYPT(zip, ?) AS zip ';
$SQL .= 'FROM patrons p, departments d ';
$SQL .= 'WHERE department = d.deptID ';
$SQL .= 'AND uniqueID = ?';
$query = $DB->prepare($SQL);
$p = array(
    $key,
    $key,
    $key,
    $key,
    $key,
    $key,
    $key,
    $key,
    $key,
    $key,
    $key,
    $uid,
);
$query->execute($p);
$result = $query->fetch();
// dump the results
var_dump($result);
print "'n'n";
// And any error info
var_dump($DB->errorInfo());
exit;

以下是正常工作时的样本输出：

// Salted is true
bool(true)
// UID is:
string(64) "52223d99e1db275716028cf6fd4f58895b1df7eb8e061cefab346b8ce3cf4ff4"
// It was not double-salted:
string(64) "52223d99e1db275716028cf6fd4f58895b1df7eb8e061cefab346b8ce3cf4ff4"
// Results were:
array(46) {
  ["patronID"]=>
  string(1) "126"
  [0]=>
  string(1) "126"
  ["uniqueID"]=>
  string(64) "52223d99e1db275716028cf6fd4f58895b1df7eb8e061cefab346b8ce3cf4ff4"
  [1]=>
  string(64) "52223d99e1db275716028cf6fd4f58895b1df7eb8e061cefab346b8ce3cf4ff4"
  ["status"]=>
  string(1) "4"
  [2]=>
  string(1) "4"
  ["active"]=>
  string(1) "1"
  [3]=>
  string(1) "1"
  *** snip! ***
  [21]=>
  string(2) "TX"
  ["zip"]=>
  string(5) "78623"
  [22]=>
  string(5) "78623"
}
// Errors reported?
array(1) {
  [0]=>
  string(5) "00000"
}

以下是失败时的样本输出：

 // Salted is true
bool(true)
// UID is:
string(64) "1d6fa3b897b07301a836f5441d23f60e7cb4b52a00ee6d20648fe51b01c769bf"
// It was not double salted
string(64) "1d6fa3b897b07301a836f5441d23f60e7cb4b52a00ee6d20648fe51b01c769bf"
// Results were:
bool(false)
// Error code was:
array(1) {
  [0]=>
  string(5) "00000"
}

我不明白为什么它对某些uid有效，但对其他uid无效。此外，在第二个示例中，结果集显示FALSE，但数据库报告错误00000，意思是"没有错误"。我已经检查了查询是否准备妥当，在这两种情况下都是这样。

我在这里错过了什么？