Notice: Undefined index: ошибка

<?php
 
function fn_print_result($link, $sql) 
{
    if ($result = mysqli_query($link, $sql)) {
        if (mysqli_num_rows($result) > 0) {
        echo "<table>";
            echo "<tr>";
                echo "<th>id</th>";
                echo "<th>first_name</th>";
                echo "<th>last_name</th>";
                echo "<th>email</th>";
                echo "<th>group_id</th>";
                echo "<th>group</th>";
                echo "<th>group_status</th>";
            echo "</tr>";
        while ($row = mysqli_fetch_array($result)) {
            echo "<tr>";
            echo "<td>" . $row['id'] . "</td>";
            echo "<td>" . $row['first_name'] . "</td>";
            echo "<td>" . $row['last_name'] . "</td>";
            echo "<td>" . $row['email'] . "</td>";
            echo "<td>" . $row['group_id'] . "</td>";
            echo "<td>" . $row['group_name'] . "</td>";
            echo "<td>" . $row['group_status'] . "</td>";
            echo "</tr>";
        }
        echo "</table>";
        mysqli_free_result($result);
    } else {
        echo "No records matching your query were found.";
        }
    } else {
        "ERROR: Could not able to execute $sql. " . mysqli_error($link);
    }
}
?>

<?php
require_once("main_db.php");
require_once("print_result1.php");
 
$inner_join = "SELECT users.first_name, users.last_name, usergroups.name
    FROM users INNER JOIN usergroups
    ON users.usergroup_id = usergroups.id";
 
 
    fn_print_result($link, $inner_join);
  
    
mysqli_close($link);