PHP : Using a variable to hold a table name, and using that variable in queries [duplicate]

Question

I am currently learning PHP, and I'm working on a Registration Form. Somewhere in my code I have these statements

$query = "SELECT `stud_no` FROM `tb_registered_users` WHERE `stud_no`='$studno'";

and

$query = "INSERT INTO `tb_registered_users`
VALUES ('".$studno."','".$firstname."','".$lastname."')";

but instead I want to declare this variable and use it in the queries mentioned above

$mysql_tb = 'tb_registered_users';

So what is the correct syntax for this?

Answer 1

$query = "INSERT INTO `" . $mysql_tb . "`
VALUES ('".$studno."','".$firstname."','".$lastname."')";

Answer 2

<?php
$mysql_tb = 'tb_registered_users';
$query = "SELECT `stud_no` FROM `{$mysql_tb}` WHERE `stud_no`='$studno'";
$query = "INSERT INTO `{$mysql_tb}` VALUES ('".$studno."','".$firstname."','".$lastname."')";