How to retrieve data from multiple tables using a PHP form

Question

I want to retrieve data from multiple tables using dot operator/join where arguments are passed from an HTML/PHP form.

HTML CODE

<input name="rollno" type="text" placeholder="Roll Number" required>
<input name="submit_view_details" type="submit" value="Proceed">

PHP CODE

if(isset($_POST['submit_view_details']))
{
    $rollno = (int) $_POST['rollno'];
    $query = "select * from table1, table2 where table1.{$rollno}=table2.{$rollno}";
    $result=mysqli_query($connection,$query);
}

Can someone please help me with this?