Login, please.
<form action="order.php"  method="post">
<input type="text" name="name" value="">
<input type="text" name="pwd" value="">
<input type="submit" name="submit" value="Click to rent a car!">
</form>


update carst set isfree=0;
update carst set isfree=1
where id in
(select id_c from orderst where o_to is null);

select type from carst  where (id in
(select id_c from orderst where o_to is null))
or (id not in (select id_c from orderst));

http://iat.fs.cvut.cz/web/cv/post3.php

insert into orderst (id_c,id_u,o_from,km1) values(7,3,now(),123456);

select id from userst where login='bock' and pwd='john';