php登陆小疑点

php登陆小问题
login.php

PHP code

<!--

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--><script type="text/javascript">
    function check()
    {
        var un = document.getElementById("username").value;
        var up = document.getElementById("userpass").value;
        if(un==""){alert("null"); return false;}
        if(up==""){alert("null");return false;}
        
    }
</script>

用户名：
密 码：

show.php

PHP code

<!--

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--><?php include("conn.php"); ?>
<?php if($_POST["submit"])
    {
        echo $sql ="select * from users where username='".$_POST["username"]."' and userpass='".$_POST["userpass"]."'";
        $result=mysql_query($sql);
        //echo count($result);
        
        if($result)
        {
            echo "登陆成功";
        }else
        {
            echo "不要捣乱";
        }
    }
?>

------解决方案--------------------
if($result) $result不为0则if时默认为true