Sqlite SQL Statement Not Working As I Expecting - sql

Question

Im using sqlite3 database and i try to get data from two table with cross join.
They have some foreign keys and i can`t get reference value
for currency names (b_currency and s_currency).
They need to be like 'USD','EUR','TRL' etc.
SQL STATEMENT:
select
a.pid,
person.fullname,
a.amount as b_amount,
b.amount as s_amount,
a.currency as b_currency,
b.currency as s_currency,
a.rate as b_rate,
b.rate as s_rate,
`user`.username,
a.`date`
from buy_process as a
inner join person
on a.fullname=person.id
inner join currency
on b_currency=currency.id and s_currency=currency.id
inner join `user`
on a.`user`=`user`.id
cross join sell_process as b
where a.pid=b.pid;
BUY_PROCESS AND SELL_PROCESS TABLE FIELDS ARE SAME:
-- Describe BUY_PROCESS
CREATE TABLE `buy_process`(
id integer primary key AUTOINCREMENT,
pid VARCHAR(50) NOT NULL UNIQUE,
fullname INTEGER NOT NULL,
amount VARCHAR(50) NOT NULL,
currency INTEGER NOT NULL,
rate VARCHAR(50) NOT NULL,
`user` INTEGER NOT NULL,
`date` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
CONSTRAINT fkbuy_fullname FOREIGN KEY(fullname) REFERENCES person(id),
CONSTRAINT fkbuy_currency FOREIGN KEY(currency) REFERENCES currency(id),
CONSTRAINT fkbuy_user FOREIGN KEY(`user`) REFERENCES `user`(id)
);
RESULT:
Result image
I tried to change field names but i did not succeed:
a.pid,
person.fullname,
a.amount as b_amount,
b.amount,
currency.name as b_currency,
currency.name as s_currency,
a.rate as b_rate,
b.rate as s_rate,
`user`.username,
a.`date`
from buy_process as a
inner join person
on a.fullname=person.id
inner join currency
on b_currency=currency.id and s_currency=currency.id
inner join `user`
on a.`user`=`user`.id
cross join sell_process as b
where a.pid=b.pid;

Answer 1

I don't understand what you want to achieve with the cross join (you have a condition a.pid=b.pid, why not just inner join them?).
You need to join the currency table twice, once for the buy currency, and once for the sell currency:
select
...
b_cncy.name as b_currency,
s_cncy.name as s_currency,
...
from
buy_process as bp
inner join
sell_process as sp
on bp.pid=sp.pid
inner join
currency b_cncy
on b_cncy.id=bp.currency
inner join currency s_cncy
on s_cncy.id=sp.currency
inner join `user` usr
on usr.id=bp.`user`