PHP准备的声明我很想知道为什么这不起作用

Question

首先，我必须说我很喜欢PHP。这太有趣了。所以这是我的问题，我正在做准备好的陈述和下面的工作

<?php
$qm = $con->prepare("SELECT id, receiving_user_id, send_date, message_title, message_body, senders_name FROM Messages WHERE receiving_user_id=? ORDER by id");
/* execute statement */
$qm ->bind_param('i',$userid);
$qm->execute();
/* bind result variables */
$qm->bind_result($messid, $uid, $sent, $title, $body, $dudesname);
/* fetch values */
while ($qm->fetch()) {
    echo ($dudesname. $title." ");
}
/* close statement */
$qm->close();
/* close connection */
$sql_e = $con-> prepare("SELECT id FROM Messages WHERE receiving_user_id=?");
$sql_e -> bind_param('i', $userid);
$sql_e -> execute();
$userCheck = $sql_e -> get_result();
$sql_e -> close();
if ($userCheck -> num_rows == 0) {
    echo "No Messages... :(";
}
?>

但是，由于$sql_e语句和$qm语句所做的事情完全相同，所以我认为我可以放置以下内容，这样就可以工作了。但事实并非如此。

$qm = $con->prepare("SELECT id, receiving_user_id, send_date, message_title, message_body, senders_name FROM Messages WHERE receiving_user_id=? ORDER by id");
    /* execute statement */
    $qm ->bind_param('i',$userid);
    $qm->execute();
    /* bind result variables */
    $qm->bind_result($messid, $uid, $sent, $title, $body, $dudesname);
    /* fetch values */
    while ($qm->fetch()) {
        echo ($dudesname. $title." ");
    }
    /* close statement */
    $qm->close();
    /* close connection */

    $qm -> execute();
    $userCheck = $qm-> get_result();
    $qm -> close();
    if ($userCheck -> num_rows == 0) {
        echo "No Messages... :(";
    }

没有预先准备好的语句输入相同的内容，例如

$qm -> execute();
// Different Variables Here
$qm -> close();

$qm -> execute();
// Yet Another Set of Variables Here
$qm -> close();

怪怪的。如能对此提供任何意见，将不胜感激。我是PHP开发的新手，我正在努力学习我能学到的一切。

编辑到代码，使IT与$stmt重置()工作；

$qm = $con->prepare("SELECT id, receiving_user_id, send_date, message_title, message_body, senders_name FROM Messages WHERE receiving_user_id=? ORDER by id");
/* execute statement */
$qm ->bind_param('i',$userid);
$qm->execute();
/* bind result variables */
$qm->bind_result($messid, $uid, $sent, $title, $body, $dudesname);
/* fetch values */
while ($qm->fetch()) {
    echo ($dudesname. $title." ");
}
/* reset statement */
$qm->reset();

$qm -> execute();
$userCheck = $qm -> get_result();
if ($userCheck -> num_rows == 0) {
    echo "No Messages... :(";
}

/* close statement */
$qm -> close();

Answer 1

您不需要执行查询两次。我想这就是你想要的：

$qm = $con->prepare("SELECT id, receiving_user_id, send_date, message_title, message_body, senders_name FROM Messages WHERE receiving_user_id=? ORDER by id");
/* execute statement */
$qm ->bind_param('i',$userid);
$qm->execute();
/* bind result variables */
$qm->bind_result($messid, $uid, $sent, $title, $body, $dudesname);
/* fetch values */
$userCheck = $qm->get_result();
if ($userCheck->num_rows > 0) {
     while ($userCheck->fetch()) {
         echo $dudesname. $title . " ";
     }
} else {
     echo "No Messages... :(";
}
/* close statement */
$qm -> close();

您的当前代码提前关闭了连接。