警告：mysqli_num_rows（）预计参数1被mysqli_result，在C定的boolean：\ XAMPP \ htdocs中\ midtermProject \ signupPost.php

Question

这里是我的代码

$res = mysqli_query($conn, "SELECT * FROM foodtography WHERE email = '$email'"); 

     if(mysqli_num_rows($res) != 0) { 
      $response = 'email already taken'; 
     } 

     $res = mysqli_query($conn, "SELECT * FROM foodtography WHERE name = '$name'"); 

     if(mysqli_num_rows($res) != 0) { 
      $response = 'Name already in use'; 
     } 

     $res = mysqli_query($conn, "SELECT * FROM foodtography WHERE username = '$uname'"); 

     if(mysqli_num_rows($res) != 0){ 
      $response = 'Username not available'; 
     } 

Answer 1

这是因为下面的计算结果为false

$res = mysqli_query($conn, "SELECT * FROM foodtography WHERE name = '$name'"); 

这可能是因为您的查询中有错误。这可能是因为$ name是空的或具有无效字符。我们都知道的错误实际上可能来自

$res = mysqli_query($conn, "SELECT * FROM foodtography WHERE email = '$email'"); 

或

$res = mysqli_query($conn, "SELECT * FROM foodtography WHERE username = '$uname'") 

你还没告诉我们的行号。你不应该这样使用mysqli。您应该使用准备好的语句并绑定参数以避免此类错误并避免sql注入。