mysql_fetch_array期望参数1是资源

Question

任何人都可以看到任何错误，也不会为我运行时不断收到错误和其他一些东西，如果有人能指出我正确的方向，我会很感激

mysql_connect("$host", "$username", "$password")or die("cannot connect"); 
mysql_select_db("$db_name")or die("cannot select DB");


$id=$_POST['id'];


$sql="SELECT MAX(a_id) AS Maxa_id FROM $tbl_name WHERE question_id='$id'";
$result=mysql_query($sql);
$rows=mysql_fetch_array($result);


if ($rows) {
$Max_id = $rows['Maxa_id']+1;
}
else {
$Max_id = 1;
}


$a_name=$_POST['a_name'];

$a_answer=$_POST['a_answer']; 

$datetime=date("d/m/y H:i:s"); 

Answer 1

阅读http://pl1.php.net/manual/pl/function.mysql-query.php

mysql_query只能返回false

$sql="SELECT MAX(a_id) AS Maxa_id FROM $tbl_name WHERE question_id='$id'";

你确定$ tbl_name已设置？