未定义变量php更新mysql数据

这是试图更新mysql数据错误的代码，说明未定义的变量

mysql_connect ("localhost", "root", "");
mysql_select_db("supplierdetails");
 $con = mysql_connect("localhost", "root", "");
   if (!$con)
    {
    die('Could not connect: ' . mysql_error());
    }
//Run a query 
    $result = mysql_query ("SELECT * FROM users WHERE id= '$id'");
    while ($row = mysql_fetch_array($result))
   {
$username=$row['username'];
$password=$row['password'];
  }
$query = "UPDATE users SET username = '$username', password = '$password' WHERE id           = '$id'";
$result = @mysql_query($query);
//Check whether the query was successful or not
if($result) {  
    header("message= Users Updated");
}else {
    die("Query failed");
}
?>

---

您使用了2

connect

无需执行

而
却忘记了
$id

mysql_connect ("localhost", "root", "");
mysql_select_db("supplierdetails");
 $con = mysql_connect("localhost", "root", "");
   if (!$con)
    {
    die('Could not connect: ' . mysql_error());
    }
//Run a query 
    $result = mysql_query ("SELECT * FROM users WHERE id= '$id'");
    while ($row = mysql_fetch_array($result))
   {
$username=$row['username'];
$password=$row['password'];
  }
$query = "UPDATE users SET username = '$username', password = '$password' WHERE id           = '$id'";
$result = @mysql_query($query);
//Check whether the query was successful or not
if($result) {  
    header("message= Users Updated");
}else {
    die("Query failed");
}
?>

    $con = mysql_connect("localhost", "root", "");
    mysql_select_db("supplierdetails");

       if (!$con)
        {
        die('Could not connect: ' . mysql_error());
        }

    $id = $_POST['id'];        
    $username=$_POST['username'];
    $password=$_POST['password'];

    $query = "UPDATE users SET username = '".$username."', password = '".$password."' WHERE id = '".$id."'";
    $result = mysql_query($query);
    //Check whether the query was successful or not
    if($result) {  
        echo "message= Users Updated";
    }else {
        die("Query failed");
    }
    ?>

你错过了$id值吗

mysql_connect ("localhost", "root", "");
mysql_select_db("supplierdetails");
 $con = mysql_connect("localhost", "root", "");
   if (!$con)
    {
    die('Could not connect: ' . mysql_error());
    }
//Run a query 
    $result = mysql_query ("SELECT * FROM users WHERE id= '$id'");
    while ($row = mysql_fetch_array($result))
   {
$username=$row['username'];
$password=$row['password'];
  }
$query = "UPDATE users SET username = '$username', password = '$password' WHERE id           = '$id'";
$result = @mysql_query($query);
//Check whether the query was successful or not
if($result) {  
    header("message= Users Updated");
}else {
    die("Query failed");
}
?>

并且可以使用
echo
调试或检查脚本结果，而不是
header

mysql_connect ("localhost", "root", "");
mysql_select_db("supplierdetails");
 $con = mysql_connect("localhost", "root", "");
   if (!$con)
    {
    die('Could not connect: ' . mysql_error());
    }
//Run a query 
    $result = mysql_query ("SELECT * FROM users WHERE id= '$id'");
    while ($row = mysql_fetch_array($result))
   {
$username=$row['username'];
$password=$row['password'];
  }
$query = "UPDATE users SET username = '$username', password = '$password' WHERE id           = '$id'";
$result = @mysql_query($query);
//Check whether the query was successful or not
if($result) {  
    header("message= Users Updated");
}else {
    die("Query failed");
}
?>

http://php.net/manual/en/function.header.php
请更具体地说明未定义的变量

mysql_connect ("localhost", "root", "");
mysql_select_db("supplierdetails");
 $con = mysql_connect("localhost", "root", "");
   if (!$con)
    {
    die('Could not connect: ' . mysql_error());
    }
//Run a query 
    $result = mysql_query ("SELECT * FROM users WHERE id= '$id'");
    while ($row = mysql_fetch_array($result))
   {
$username=$row['username'];
$password=$row['password'];
  }
$query = "UPDATE users SET username = '$username', password = '$password' WHERE id           = '$id'";
$result = @mysql_query($query);
//Check whether the query was successful or not
if($result) {  
    header("message= Users Updated");
}else {
    die("Query failed");
}
?>

在您发布的代码中，
$username
和
$password
仅在
$result
返回结果时设置，如果不返回结果，则您的
while
循环将不会运行，因此将永远不会设置
$username
和
$password

mysql_connect ("localhost", "root", "");
mysql_select_db("supplierdetails");
 $con = mysql_connect("localhost", "root", "");
   if (!$con)
    {
    die('Could not connect: ' . mysql_error());
    }
//Run a query 
    $result = mysql_query ("SELECT * FROM users WHERE id= '$id'");
    while ($row = mysql_fetch_array($result))
   {
$username=$row['username'];
$password=$row['password'];
  }
$query = "UPDATE users SET username = '$username', password = '$password' WHERE id           = '$id'";
$result = @mysql_query($query);
//Check whether the query was successful or not
if($result) {  
    header("message= Users Updated");
}else {
    die("Query failed");
}
?>

另外，
$id
看起来也不像是已经设置的，除非这是在您的问题中包含的代码之外设置的

mysql_connect ("localhost", "root", "");
mysql_select_db("supplierdetails");
 $con = mysql_connect("localhost", "root", "");
   if (!$con)
    {
    die('Could not connect: ' . mysql_error());
    }
//Run a query 
    $result = mysql_query ("SELECT * FROM users WHERE id= '$id'");
    while ($row = mysql_fetch_array($result))
   {
$username=$row['username'];
$password=$row['password'];
  }
$query = "UPDATE users SET username = '$username', password = '$password' WHERE id           = '$id'";
$result = @mysql_query($query);
//Check whether the query was successful or not
if($result) {  
    header("message= Users Updated");
}else {
    die("Query failed");
}
?>

希望这有帮助：）
在查询中使用
$id之前，我看不到您在任何地方定义它。注意：未定义变量：第10行E:\xampp\htdocs\Edit_User.php中的id注意：未定义变量：第16行E:\xampp\htdocs\Edit_User.php中的用户名注意：未定义变量：第10行E:\xampp\htdocs\Edit_User.php中的密码16注意：未定义的变量：在第16行的E:\xampp\htdocs\Edit\u User.php中的id*我有一个User\u Edit\u表单，其中包含以下内容code@NatalieWebb您是否获得了$u GET['id']的价值？请呼出$\u GET。您在这里真正想要实现的是什么？据我所见，您正在检索用户详细信息，然后仅使用相同的值更新该用户详细信息：|
mysql_connect ("localhost", "root", "");
mysql_select_db("supplierdetails");
 $con = mysql_connect("localhost", "root", "");
   if (!$con)
    {
    die('Could not connect: ' . mysql_error());
    }
//Run a query 
    $result = mysql_query ("SELECT * FROM users WHERE id= '$id'");
    while ($row = mysql_fetch_array($result))
   {
$username=$row['username'];
$password=$row['password'];
  }
$query = "UPDATE users SET username = '$username', password = '$password' WHERE id           = '$id'";
$result = @mysql_query($query);
//Check whether the query was successful or not
if($result) {  
    header("message= Users Updated");
}else {
    die("Query failed");
}
?>