How to “close” database when the query happens?

$database->count = "SELECT * FROM table WHERE item_id = 1"

if($database->count == 1)
{
   $database->update = "UPDATE users SET money = money - 1000";
   $database->delete = "DELETE table WHERE item_id = 1";
}

Let's say I have this code (I've just created it) in index.php page. Can at the same time "SELECT * FROM table WHERE item_id = 1" query happen so two people would get count 1 and -1000 money? If yes, how can I avoid that?

Thank you.