Why do I get a connection error when querying SQL through the body of a PHP function?

Question

PHP

I am suffering with such a problem: I need to get the value of this radio when clicking on the radio and pass it to the SQL query. In JS, I am getting a value.

$("input[name='select_account']").on('click', function () {
    var x = $("input[name='select_account']:checked").val();
})

Then, as I understand it, it must be transferred to PHP and made a request via SQL. Accordingly, I make a function that passes this value, but when I receive a request, I get an error (Query failed). However, if I run the request code outside of the function body, no error occurs.

function sql_query($user_id) {
    $query = 'select * from users WHERE id='.$user_id.';';
    $query_result = mysqli_query($connection, $query);
        if(!$query_result) {
            die('Query failed'.mysqli_error());
        } else {
            echo ('Complete');
        }
        return $query_result;
}

$connection I get earlier in the code with no error.

And in general, maybe I'm suffering in vain with this function, maybe there is a simpler solution?

Answer 1

You have something <?=inside the php code.

Answer 2

PHP's main problem is that all online textbooks contain horror from the last century. And the saddest thing is that users of the AUser0 type repeat it mindlessly.
Here is the correct way:

function get_user($connection, $user_id) {
    $stmt = $connection->prepare('select * from users WHERE id=?');
    $stmt->bind_param("s", $user_id); 
    $stmt->execute();
    return $stmt->get_result()->fetch_assoc();
}