How to select from 2 FB SQL tables with foreign keys?

Question

I have 2 tables created like the following:

create table accounts(
accountOID int primary key not null,
bankcodenumber int,
accountnumber int
);

create table user(
userOID int primary key not null,
name varchar(25),
accountOID0 int,
accountOID1 int
);

Each user has 1 or 2 accounts, so to declare the foreign keys I type this:

alter table user add foreign key(accountOID0) references account(accountOID);

alter table user add foreign key(accountOID1) references account(accountOID);

Now, how can I list the accounts like this:

Name    | Bankcodenumber | Accountnumber
Sanchez | 0123456789     | 547
Trent   | 1234567890     | 278
Sanchez | 2345678901     | 480
Carlson | 3435577890     | 503
Jackson | 6833556904     | 168
...     | ...            | ...

I have tried this but with no success:

select name, (select bankcodenumber, accountnumber from account
where user.accountOID0 = accountOID or user.accountOID1 = accountOID)
from user order by name;

Answer 1

You seem to want union all :

select u.name, a.Bankcodenumber, a.Accountnumber
from user u join
     account a
     on u.accountoid0 = a.accountoid
union all
select u.name, a.Bankcodenumber, a.Accountnumber
from user u join
     account a
     on u.accountoid1 = a.accountoid;

Answer 2

SELECT u.name,
       a.bankcodenumber,
       a.accountnumber 
  FROM user u
INNER JOIN 
       accounts a
    ON u.accountOID0 = a.accountOID
UNION
SELECT u.name,
       a.bankcodenumber,
       a.accountnumber 
  FROM user u
INNER JOIN 
       accounts a
    ON u.accountOID1 = a.accountOID; 

Answer 3

An option without UNION but using a single SELECT with joins:

http://sqlfiddle.com/#!5/17ccc/1/0

select
   Coalesce(u1.name, u0.name) as name1,
   a.bankcodenumber,
   a.accountnumber
 from accounts a
   left join users u0
     on u0.accountOID0 = a.accountOID
   left join users u1
     on u1.accountOID1 = a.accountOID
 where name1 is not null

It uses the topicstarter's example data entered as

create table accounts(
accountOID int primary key not null,
bankcodenumber int,
accountnumber int
);

create table users(
userOID int primary key not null,
name varchar(25),
accountOID0 int references accounts(accountOID),
accountOID1 int references accounts(accountOID)
);

insert into accounts values (1, 0123456789, 547);
insert into accounts values (2, 1234567890, 278);
insert into accounts values (3, 2345678901, 480);
insert into accounts values (4, 3435577890, 503);
insert into accounts values (5, 6833556904, 168);

insert into users values(1, 'Trent', NULL, 2);
insert into users values(2, 'Carlson', 4, NULL);
insert into users values(3, 'Sanchez', 3, 1);
insert into users values(4, 'Jackson', 5, NULL);

It might loose some data if there are cases when one user's accountOID0 is equal to another user's accountOID1 . But the topicstarter implies there should be no such cases. Though he also does not say if there are some constraints or other guards to ensure that would never happen.