LEFT JOIN trouble with multiple tables - postgresql

Question

I have the following query
SELECT a.account_id, sum(p.amount) AS amount
FROM accounts a
LEFT JOIN users_accounts ua
JOIN users u
JOIN payments p on p.meta_id = u.user_id
ON u.user_id = ua.user_id
ON ua.account_id = a.account_id
WHERE p.date_prcsd BETWEEN '2017-08-01 00:00:00' AND '2017-08-31 23:59:59'
GROUP BY a.account_id
ORDER BY account_id ASC;
What I want is all the rows from accounts a and zeroes for missing amount data. Same result set for different types of joins and different join structures - only rows that have some payments in p.
Where do I go wrong?

Answer 1

Simplified:
SELECT a.account_id
,sum(coalesce(p2.amount, 0)) AS amount
FROM accounts a
LEFT JOIN users_accounts ua ON (a.account_id = ua.account_id)
LEFT JOIN users u ON (ua.user_id = u.user_id)
LEFT JOIN (
SELECT p.meta_id
,p.amount
FROM payments p
WHERE p.date BETWEEN '2017-08-01' AND '2017-08-10'
) AS p2 ON (u.user_id = p2.meta_id)
GROUP BY a.account_id
ORDER BY account_id ASC;
Result:
account_id | amount
------------+--------
1 | 4
2 | 0
3 | 0
(3 rows)
Explanation: you need to take care of all returning null values. coalesce() does that for you. The where-clause is actually the real problem in your solution because it filters out rows that you would want to have in your endresult. On top of that: you left out the left join for the other tables. I created a simplified test db:
$ cat tables.sql
drop table users_accounts;
drop table payments;
drop table users;
drop table accounts;
create table accounts (account_id serial primary key, name varchar not
null);
create table users (user_id serial primary key, name varchar not null);
create table users_accounts(user_id int references users(user_id),
account_id int references
accounts(account_id));
create table payments(meta_id int references users(user_id), amount int
not null, date date);
insert into accounts (account_id, name) values (1, 'Account A'), (2,
'Account B'), (3, 'Account C');
insert into users (user_id, name) values (1, 'Marc'), (2, 'Ruben'), (3,
'Isaak');
insert into users_accounts (user_id, account_id) values (1,1),(2,1);
insert into payments(meta_id, amount, date) values (1,1, '2017-08-01'),
(1,2, '2017-08-11'),(1,3, '2017-08-03'),(2,1, null),(2,2, null),(2,3,
null);