PHP Update MySQL, form input coming through as column name - php

Question

So I am sorry as I feel I ask stupid questions a lot. I am learning as I go but getting there.
I've created a basic HTML form and with the help of a previous answer I've made the PHP and MySQL query. However when I submit the form the input values from the form come up as column names rather than the information to be updated in the row.
In simple terms when the form is submitted if the input is to change first name from James to Josh the error message is:
"Error updating record: Unknown column 'Josh' in 'field list'"
I though in my SQL query below it would pick up the column name as first_name but this is obviously not happening.
<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "Users";
//Create variables
$first_name=$_POST['first_name'];
$last_name=$_POST['last_name'];
$ID=$_POST['ID'];
// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql = "UPDATE Users SET first_name=$first_name, last_name=$last_name WHERE
ID=$ID";
if ($conn->query($sql) === TRUE) {
echo "Record updated successfully";
} else {
echo "Error updating record: " . $conn->error;
}
$conn->close();
?>

Answer 1

I don't know PHP, but I suspect that your problem is that you arent't quoting the value in your update statment. So try something like:
"UPDATE Users SET first_name='$first_name', last_name='$last_name' WHERE ID=$ID"