帮找找语句毛病？

[frydragon]

$ll=mysql_query("select * from student_info where Username=\"$Username\"");
echo mysql_num_rows($ll);

打印结果本应为1，却老是0

[lovejsp]

select *from student_info where username='$username'

[zxyufan]

$ll=mysql_query("select * from student_info where Username='".$Username."'");

[frydragon]

$ll=mysql_query("select * from student_info where Username='".$Username."'");
echo mysql_num_rows($ll);
原文是这样，还是不行，咋办？

[zxyufan]

$sql="select * from student_info where Username='".$Username."'";
echo $sql;
$res = mysql_query($sql);
echo "<br>";
echo mysql_num_rows($res);

[caoz]

先执行echo $ll，看看出什么，然后到mysql里执行显示的东东，
这是基本程序调试的策略。