为什么在php中没有返回结果，但是在mysql中有？

Question

查询：

SELECT * FROM ac_journal WHERE datetime < (SELECT datetime FROM ac_journal WHERE jid = 1089 AND rid IN ('2','3','4')) ORDER BY datetime DESC LIMIT 1

当我在phpmyadmin中执行此查询时，我得到一行

在我的代码中，它没有返回任何内容。

function ac_journal_get_previous_entry($jid)
{
  global $user; //1
  echo $jid; //1089
  echo "<br />'" . implode("','", array_keys($user->roles)) . "'"; //'2','3','4'

  if ($jid > 0)
  {
    $result = db_query("SELECT * FROM {ac_journal} WHERE datetime < (SELECT datetime FROM {ac_journal} WHERE jid = ? AND rid IN (?)) ORDER BY datetime DESC LIMIT 1", array($jid, "'" . implode("','", array_keys($user->roles)) . "'"));
    $obj = $result->fetchAll();
    echo $result->rowCount(); //0

    if (is_array($obj) && count($obj) > 0)
    { 
      echo "HERE"; //never gets here
      return "<a href='https://example.com/journal/" . $obj[0]->jid . "'>Previous</a>";
    }
  }
}

Answer 1

我不得不改变它：

$result = db_query('SELECT * FROM {ac_journal} WHERE datetime < (SELECT datetime FROM {ac_journal} WHERE jid = :jid) AND rid IN (:rid) ORDER BY datetime DESC LIMIT 1', array(':jid' => $jid, ':rid' => array_keys($user->roles)));

Answer 2

此行不会产生echo：fetchAll();，如;

$obj = $result->fetchAll();

尝试将其更改为：

fetch(PDO::FETCH_ASSOC);

但是，在获取对象之前首先执行数组，如：

$obj->execute(array(':jid' => $jid ));
$result = $obj->fetch(PDO::FETCH_ASSOC);

if (is_array($result) && count($result) > 0){ 
     echo "HERE"
.................

来源：http://php.net/manual/en/pdostatement.fetch.php