Prepared语句返回空结果，可能是语法错误

Question

When I execute the prepared statement the results are returned empty. If I copy and paste the statement into phpMyAdmin it executes properly. $_SESSION['userGroup'] has been checked and confirmed to contain the proper value but $systems remains undefined.

Am I missing something?

        $stmt = $mysqli -> prepare("SELECT `Systems` FROM `groups` WHERE `GroupID` = ?");
            echo $mysqli -> error;

        $stmt -> bind_param('i', $_SESSION['userGroup']);
        $stmt -> execute();
        $stmt -> store_result();
        $stmt -> bind_result($systems);

Answer 1

Just try

$stmt -> bind_param('i', $_SESSION['userGroup']);
$stmt -> execute();
$stmt -> bind_result($systems);
$stmt -> fetch();