Вячеслав

$optt = (int) $_POST['id_mat'];
echo $optt;
$options = explode(";",$materialss[$optt]["option"]);

$result = $this->mysqli->query("SELECT 'id' FROM `caps` WHERE `bm_id` = '$bm_id' AND `event_id` = '$event_id'");
if ($result->num_rows > 0) {
    // do
}