SQL get latest record for each ID - sql

Question

I have three tables that contains data as below:
Users
Id Name Other_Columns
---------------------------
1 John Blah
2 Ricky Blah
3 Stella Blah
4 Bob Blah
Saldo
Id User_id Saldo
--------------------
1 3 0.00
2 1 9.00
3 2 0.15
4 4 3.50
Payments
Id User_id Amount Paid_date
------------------------------------------
1 2 10.00 2014-09-01 08:10
2 2 25.00 2014-09-01 09:00
3 3 100.00 2014-05-10 12:47
4 1 20.50 2014-02-23 15:30
How to get result like this:
Id Name Saldo Last Payment
------------------------------------------
1 John 9.00 23.02.2014 20.50
2 Ricky 0.15 01.09.2014 25.00
3 Stella 0.00 0000-00-00 0.00
4 Bob 3.50 10.05.2014 100.00
Thank you.

Answer 1

select u.id, u.name, s.saldo, p.last_paid_date, p2.amount
from users u
join saldo s
on u.id = s.user_id
join (select user_id, max(paid_date) as last_paid_date
from payments
group by user_id) p
on u.id = p.user_id
join payments p2
on p.last_paid_date = p2.paid_date
and p.user_id = p2.user_id
This answer assumes:
(1) On table SALDO, there is one row per USER_ID
(2) On table PAYMENTS, there can be multiple rows per USER_ID
(I'm pretty confident about #2 being true, I don't know about #1, as you didn't say and your sample data doesn't indicate one way or the other)