function getMentions($content) {
    global $db;
    $mention_regex = "/@+([a-zA-Z0-9-_]+)/"; //mention regrex to get all @texts
    $regexIt = preg_match_all($mention_regex, $content, $matches);
    if ($regexIt) {
         foreach ($matches[1] as $key => $match) {
             if ($key === 0) continue;
                 $mentioned[] = mysqli_real_escape_string($db, $match[0]);
                 $match_user = mysqli_query($db, "SELECT user_id, user_name FROM dot_users WHERE user_name  IN ('" . implode("','", $matches[1]) . "')") or die(mysqli_error($db));
                 $userDeti = mysqli_fetch_array($match_user, MYSQLI_ASSOC);
                 $match_search = '@' . $match . '';
                 $match_replace = '<a target="_blank" href="' . $userDeti['user_name'] . '">@' . $userDeti['user_name'] . '</a>';
                 if (isset($userDeti['user_name'])) {
                        $content = str_replace($match_search, $match_replace, $content);
                   }
            }
    }
    return $content;
}

echo $userDeti['user_name'];