เช็คล๊อคอินด้วยการเลือกแผนก + แอดมิน ช่วยดูโค๊ดหั้ยหน่อยครับ

<form id ="form1" name="form1" method="post" action="checklogin.php">
    <center><br><br>
    Username <input type="text" name="username" value=""/><br><p>
    Password <input type="password" name="password" value=""/><br><p>
    <select id="depart" name="depart1" style="width:90px">
            <option value="">- Choose -</option>
            <?
            include ("mysql_connect.php");
            $strSQL = "SELECT * FROM department ORDER BY id_department ASC ";
            $objQuery = mysql_query($strSQL) or die ("Error Query [".$strSQL."]");
            while($objResult = mysql_fetch_array($objQuery))
            {
            ?>
            <option value="<?=$objResult["id_department"];?>"><?=$objResult["section"];?></option>
            <?
            }
            ?>
            </select>
            <br><p>
    <input type="submit" name="submit" value="Login"/>
    </center>
    </form>

<?php
        session_start();
        include ("mysql_connect.php");
        $user = $_POST["username"];
        $pass = $_POST["password"];
        $depart = $_POST["depart1"];

        if(empty($user)){
        echo "<script>alert('Please input your username');window.location = 'form.php';</script>";
        exit();
        }
        if(empty($pass)){
        echo "<script>alert('Please input your password');window.location = 'form.php';</script>";
        exit();
        }
        if(empty($depart)){
        echo "<script>alert('Please input your choose department');window.location = 'form.php';</script>";
        exit();
        }

        $sql = "SELECT (username,password,id_department) FROM member WHERE username='$user' and password='$pass' and id_department='$depart'";
        $result = mysql_query($sql) or die ("SQL ERROR!!");  Error ตรงเน้ครับ
        $row = mysql_fetch_array($result);
        $num = mysql_num_rows($num);
        if($num ==0){
            echo "<script> alert('ชื่อหรือหรัสผ่านไม่ถูกต้อง กรุณาตรวจสอบ')";
            echo "<meta http-equiv='refresh' content='1 ; url=form.php' > ";
        }else{
            
        }
        ?>