$users = [
'u101',
'u402',
'u503',
'u703',
'u114',
'u148',
'u152',
'u173',
'u134'
];
$string = implode(" OR ", $users); // u101 OR u402 OR u503 OR u703 OR u114 OR u148 OR u152 OR u173 OR u134;
"... WHERE `akk` IN (" . implode(",", $users) . ");";