是否可以将此INSERT查询连接到if语句中？

I'm having a few issues with this silly query, was wondering is it possible to concatenate the following INSERT query inside the IF statement and outside it as well to complete the rest of the query. So I want the $orderid to be insert within the if statement and the rest of the last 3 variables outside the IF

if(isset($_POST['Submit'])){

    $orderid=mysql_insert_id();

    $sql = mysql_query("SELECT * FROM course WHERE serial='$serial'") or die(mysql_error()); 
    $fetch = mysql_fetch_assoc($sql);
    $serial = $fetch['serial'];
    $price = $fetch['price'];

    mysql_query("INSERT into course_order_detail values ('$orderid','$serial','1','$price')") or die(mysql_error()); 

}

Oh and $orderid is from the previous insert query written in my code.

Try Like this

if(isset($_POST['Submit'])){

    $orderid=mysql_insert_id();

    $sql = mysql_query("SELECT * FROM course WHERE serial='$serial'") or die(mysql_error()); 
    $fetch = mysql_fetch_assoc($sql);
    $serial = $fetch['serial'];
    $price = $fetch['price'];

    $in = mysql_query("INSERT into course_order_detail values ('$orderid')") or die(mysql_error()); 
    $new_id = mysql_insert_id();
}

$up = mysql_query("UPDATE course_order_detail SET serial='$serial',quantity='1',price='$price' WHERE orderid = ".$new_id);

You can use a nested insert with select

INSERT `into course_order_detail` SELECT '$orderid', serial, '1', price FROM course WHERE serial='$serial'

BTW sanitize your queries