php, Record Fetch from two tables - php

Question

we have two tables name "students" AND vouchers. we create the voucher of the fee and display voucher, and we also want to display the roll no of that particular student which was we create voucher, but we can't get the roll any of student table ... we got error,enter image description here I've added the code below
<?php if(isset($_GET['session_id'])):?>
<?php $student_session= $_GET['session_id'];?>
<?php
$stu = "select * from students where
session_id='$student_session'";
$run_stu = mysqli_query($con,$stu);
while($row = mysqli_fetch_array($run_stu)){
$stu_id = $row['student_id'];
$stu_roll = $row['roll_no'];
$stu_name= $row['s_name'];
?>
<?php
if (isset($_POST['many_voucher'])){
$student_roll = $_GET['roll_no'];
$student_session_post = $_GET['session_id'];
$fee_date = $_POST['fee_date'];
$adm_fee = $_POST['adm_fee'];
$reg_fee = $_POST['reg_fee'];
$tution_fee = $_POST['tution_fee'];
$lab_fund = $_POST['lab_fund'];
$misc_dues = $_POST['misc_fund'];
$others = $_POST['others'];
$total_amount = $_POST['total_amount'];
$due_date = $_POST['due_date'];
$remarks = $_POST['remarks'];
$query = "Insert INTO vouchers(session_id,roll_no,fee_month,adm_fee,reg_fee,tution_fee,lab_fund,misc_dues,other_dues,total_amount,due_date,remarks)
VALUES('$student_session_post','$student_roll','$fee_date','$adm_fee','$reg_fee','$tution_fee','$lab_fund','$misc_dues','$others','$total_amount','$due_date','$remarks')";
if(mysqli_query($con,$query)){
//echo "<script>alert('Run')</script>";
}else{
echo"query failed";
}
}
?>

Answer 1

try with this
<?php if(isset($_POST['many_voucher'])){
$student_roll = $stu_roll;
}
?>