Unable to insert into MySQL for select values - php

Question

I have a web application in which students are divided into "batches".
I am trying to insert student for particular batch and the batch will be chosen by user by select option. After that student is added to the particular batch, he/she will be added to stdhold table. However, it is only inserting for the first selected value of select option.
<?php
function specialCOn() {
$connew = mysqli_connect("localhost","root","");
$db = mysqli_select_db($connew,'mcqs');
return($connew);
}
if (isset($_POST['add']))
{
$namestd=$_POST['std_name'];
$batchstd=$_POST['batch'];
$FNAME=$_POST['f_name'];
$query3 = "INSERT INTO `$batchstd` VALUES('','$namestd','$FNAME')";
$rsq3 = mysqli_query(specialCOn(),$query3);
mysqli_close(specialCOn());
$queryrollno = "select rollno from `$batchstd` order by rollno desc";
$rsqrollno = mysqli_query(specialCOn(),$querrollno);
$getrollno = mysqli_fetch_array($rsqrollno);
$rollnoto = $getrollno[0];
echo "<script>alert('$batchstd')</script>";
echo "<script>alert('$rollnoto')</script>";
mysqli_close(specialCOn());
//Problem is here
$querystdhold = "INSERT INTO stdhold VALUES ($rollnoto, '$namestd', '$FNAME', '$batchstd')";
$rsqhold = mysqli_query(specialCOn(),$querystdhold);
mysqli_close(specialCOn());
if ($rsq3&&$rsqhold)
{
echo "<script> alert('Student Added.');
window.location.assign('addstudent.php');
</script>";
//header('Location:addstudent.php');
}
else
{
echo "<script> alert('You Havenot added Student.');
window.location.assign('addstudent.php');</script>";
}
}
?>

Answer 1

Try use this :
$db = new mysqli("host","user","pw","database");
$stmt = $db->prepare("INSERT INTO ? (col1,col2,col3) VALUES('',?,?)");
$stmt->bind_param('sss', $_POST['batch'], $_POST['std_name'], $_POST['f_name']);
$stmt->execute();
For the detail example you need to read the #Amber Answer how to create secured prepared statement.
Hope this'll help you.

Answer 2

Try specifying the column names in your insert query:
INSERT INTO stdhold (col1, col2, col3, col4) VALUES ($rollnoto, '$namestd', '$FNAME', '$batchstd');
For reference see the MySQL Insert documentation.