未定義的變量，不確定爲什麼

Question

<?php 
$tid = $_GET['tid']; 
$id = $_SESSION['userid']; 
$sql1 = "SELECT * FROM topics WHERE id='$tid' LIMIT 1"; 
$res1 = mysqli_query($connect, $sql1) or die(mysqli_error($connect)); 
while ($row = mysqli_fetch_array($res1, MYSQLI_ASSOC)) { 
    $title = $row['topic_title']; 
    $creator = $row['topic_creator']; 
} 
$sql = "SELECT * FROM users WHERE id='$creator' LIMIT 1"; 
$user_query = mysqli_query($connect, $sql) or die(mysqli_error($connect)); 
while ($row = mysqli_fetch_array($user_query, MYSQLI_ASSOC)) { 
    $name = $row["first"].$row["last"]; 
} 
echo $name; 
?> 

我對PHP有點新，但是我已經完成了類似這樣的事情，但是這次我收到錯誤消息。這裏的一切工作除了$ name。我檢查了我的SQL表並確保用戶存在，並且有第一個和最後一個區域。我不明白還有什麼可能是錯的。

注意：未定義的變量：在*上線路名**

謝謝。

Answer 1

試穿尺寸爲驗證碼：

<?php 
$tid = $_GET['tid']; 
$id = $_SESSION['userid']; 
$tid = mysqli_escape_string($connect, $tid); 
$sql1 = "SELECT * FROM topics WHERE id='{$tid}' LIMIT 1"; 
$res1 = mysqli_query($connect, $sql1) or die(mysqli_error($connect)); 
// Check for rows first. 
if($res1 and mysqli_num_rows($res1)){ 
    // Use if as while is pointless on LIMIT 1 
    if($row = mysqli_fetch_array($res1, MYSQLI_ASSOC)) { 
     $title = $row['topic_title']; 
     $creator = $row['topic_creator']; 

     $creator = mysqli_escape_string($connect, $creator); 
     $sql = "SELECT * FROM users WHERE id='{$creator}' LIMIT 1"; 
     $user_query = mysqli_query($connect, $sql) or die(mysqli_error($connect)); 
     // Check for rows first. 
     if($user_query and mysqli_num_rows($user_query)){ 
      // Use if as while is pointless on LIMIT 1 
      if ($row = mysqli_fetch_array($user_query, MYSQLI_ASSOC)) { 
       $name = $row["first"].$row["last"]; // NO HIT! 
      } 
      echo $name; 
     }else{ 
      echo 'no rows found (query 2).'; 
     } 
    } 
}else{ 
    echo 'no rows found (query 1).'; 
} 
?> 

可變$name是不確定的，因爲沒有達到$name = ...;線。因此，請確保您的查詢實際上返回結果$sql。它必須爲了定義$name。