JOIN inside a SELECT MAX in Postgres - postgresql

Question

I have the following query that returns these two elements.
SELECT ticket_holds.id, ticket_holds.created_at, orders.user_id, users.id, charges.payment_method
FROM ticket_holds
LEFT JOIN order_items ON order_items.id = ticket_holds.order_item_id
LEFT JOIN orders ON orders.id = order_items.order_id
LEFT JOIN users ON users.id = orders.user_id
LEFT JOIN charges on charges.order_id = orders.id;
This result is okay.
id | created_at | user_id | id | payment_method
----+----------------------------+---------+----+----------------
1 | 2017-05-26 04:29:22.189628 | 4 | 4 |
2 | 2017-05-26 04:33:00.721404 | 4 | 4 | some_payment_method
When I try to filter the query to display the last record created per user it also works okay using SELECT MAX.
SELECT ticket_holds.id, ticket_holds.created_at, orders.user_id, users.id, charges.payment_method
FROM ticket_holds
LEFT JOIN order_items ON order_items.id = ticket_holds.order_item_id
LEFT JOIN orders ON orders.id = order_items.order_id
LEFT JOIN users ON users.id = orders.user_id
LEFT JOIN charges on charges.order_id = orders.id
WHERE ticket_holds.created_at = (SELECT MAX(ticket_holds.created_at) FROM ticket_holds WHERE orders.user_id = users.id);
And the result
id | created_at | user_id | id | payment_method
----+----------------------------+---------+----+----------------
2 | 2017-05-26 04:33:00.721404 | 4 | 4 | some_payment_method
(1 row)
However, when Im trying to filter to only select items without a payment_method I get no results.
SELECT ticket_holds.id, ticket_holds.created_at, orders.user_id, users.id, charges.payment_method
FROM ticket_holds
LEFT JOIN order_items ON order_items.id = ticket_holds.order_item_id
LEFT JOIN orders ON orders.id = order_items.order_id
LEFT JOIN users ON users.id = orders.user_id
LEFT JOIN charges on charges.order_id = orders.id
WHERE ticket_holds.created_at = (SELECT MAX(ticket_holds.created_at) FROM ticket_holds WHERE orders.user_id = users.id AND charges.payment_method IS NULL);
(Notice the AND charges.payment_method IS NULL) and the end of the query)
This is what I get instead
id | created_at | user_id | id | payment_method
----+------------+---------+----+----------------
(0 rows)
Any idea how can I retrieve the elements with no payment method, in this case would be the record with id 1?

Answer 1

As per discussion on chat. i think below query will help you to get required result.
with data as ( SELECT ticket_holds.id, ticket_holds.created_at, orders.user_id, users.id, charges.payment_method
FROM ticket_holds
LEFT JOIN order_items ON order_items.id = ticket_holds.order_item_id
LEFT JOIN orders ON orders.id = order_items.order_id
LEFT JOIN users ON users.id = orders.user_id
LEFT JOIN charges on charges.order_id = orders.id
where charges.payment_method is null
)
select * from data d1
where d1.created_at = (select max(created_at) from data d2
where d1.users_id = d2.user_id
)
There are few points while writing an sub query in where clause. Join your table carefully as in your case you are not utilizing any column for joining.