$idarr=array(1,2,3,4,5,6,7,8,9,11,12,13,14);

$str='';
foreach(array_chunk($idarr, 5) as $val){
    $t='';
	foreach($val as $v){
		$t.=$v.',';
	}
	$t=rtrim($t,',');
	$str.="user_id in(".$t.") or ";
}
$str=trim($str,' or');
// echo $str; user_id in(1,2,3,4,5) or user_id in(6,7,8,9,11) or user_id in(12,13,14)
$s="update mina2_user set user_isexport=2 where ".$str;
echo $s;
//update tb set isexport=2 where user_id in(1,2,3,4,5) or user_id in(6,7,8,9,11) or user_id in(12,13,14)