create schema hw4;

create table hw4.cars (
    id serial primary key,
    model varchar(255) not null,
    price int not null,
    count int default 0    
    );

--
--

insert into hw4.cars(model,price,count) values 
   ('BMW',10000,50),
   ('ROLLS ROYCE',20000,10),
   ('TOYOTA',8000,1000),
   ('MERCEDEZ',1000,40),
   ('SUPRA',12000,15);

select * from hw4.cars;

--user create

create table hw4.users(
   id serial primary key,
   fullname varchar(255),
   balance int not null
);

insert into hw4.users(fullname,balance) values 
   ('user1',100000),
   ('user2',200000),
   ('user3',80000),
   ('user4',10000),
   ('user5',120000);

-- first function...

create or replace function get_price_car(min_price int)
   returns table(id int, model varchar(255), price int, count int)
   language plpgsql
  as
$$
begin
   return query
   select
   c.id,
   c.model,
   c.price,
   c.count from hw4.cars as c
   where c.price > min_price order by price ASC;
end;
$$;

select * from get_price_car(8000);

-- second function...

create or replace function get_car_id(car_id int)
   returns text
   language plpgsql
  as
$$
declare car_list text;
begin
   select concat(  
   'id: ', c.id,
   ', model: ', c.model,
   ', price: ', c.price,
   '. count: ', c.count)
   into car_list
   from hw4.cars as c
   where c.id = car_id;
   return car_list;
end;
$$;

select * from get_car_id(1);

--procedure

create or replace procedure buy_car(car_id int, car_count int, user_id int)
language plpgsql
as
$$
declare
    car_price int;
    car_count_available int;
    user_balance int;
begin
    select price, count into car_price, car_count_available
    from hw4.cars
    where id = car_id;

    if car_price is null or car_count_available is null then
        raise notice 'mashina topilmadi';
        rollback;
        return;
    end if;

    select balance into user_balance
    from hw4.users
    where id = user_id;

    if user_balance is null then
        raise notice 'foydalanuvchi topilmadi';
        rollback;
        return;
    end if;

    if user_balance < car_count * car_price then
        raise notice 'foydalanuvchining balansida yetarli pul topilmadi';
        rollback;
        return;
    end if;

    if car_count_available < car_count then
        raise notice 'mashinadan buncha emas';
        rollback;
        return;
    end if;

    update hw4.cars
    set count = count - car_count
    where id = car_id;

    update hw4.users
    set balance = balance - car_count * car_price
    where id = user_id;

    select balance into user_balance
    from hw4.users
    where id = user_id;

    if user_balance < 5 then
        raise notice 'foydalanuvchining balansida minimal summa 5 som dan kam';
        rollback;
        return;
    end if;

    commit;

    raise notice 'buyurtma muvaffaqiyatli amalga oshirildi. % ta mashina sotib olindi', car_count;
end;
$$;

call buy_car(1,2,1);

Kodingda try bor-u, lekin hayotingda catch ishlamayapti. Xatolarni to‘g‘rilash o‘rniga, ularni "feature" deb nomlab qo‘yayotgan backendchisan. Katta loyihalar qilishni orzu qilasan, lekin hozircha faqat res.send("Hello World") bilan yuribsan.

Sen o‘zingni zo‘r deb bilasan, lekin MongoDB'dagi dokumentlar sendan mustahkamroq qaror qabul qiladi. Frontendni yomon ko‘rasan, chunki sen qilgan API-larga hech kim request yubormaydi. Aslida esa backendchilar ham frontendchilar kabi "loading..." holatida yashaydi.

Xo‘jayin, sen senior bo‘lishni orzu qilasan, lekin GitHub commitlaring "Initial commit" bilan tugagan. Agar sening dasturlash yo‘lingni "ping" qilib tekshirsak, request timeout berib ketadi.

Lekin sendan yaxshi backendchi chiqadi!"