SQL Three table join - sql

Question

I haven't been able to solve this problem for several days now and I'm hoping you can help.
I'm trying to write a query that returns all the information about a stock and the last time it was updated. I would like to filter the results based on the parameter #date and return only the stocks which it's latests update is less than the supplied #date parameter. I also need the stocks with a timestamp of null so I know that theses stocks need to be updated. I have the follwing three tables that I'm working with:
stocks
- id
- asset_id
- market_id
- name
- symbol
- IPOYear
- sector
- industry
updates
- id
- [timestamp]
stock_updates
- stock_id
- update_id
I've been using the following query and it was working well for me until I realized it dosen't work if the stock doesn't have an update
select * from stocks s
where #date < (
select top 1 u.timestamp from
updates u,
stock_updates su
where
s.id = su.stock_id and
u.id = su.update_id
order by u.timestamp desc
)
So after some research I came accross outer joins and I think it's what I need to fix my problem I just haven't been able to construct the correct query. The closest I've come is the following, but it returns a record for each time the stock was updated. Thanks in advance for your help!
This is where I'm at now:
select * from stocks s
left outer join stock_updates su on s.id = su.stock_id
left outer join updates u on u.id = su.update_id
where u.[timestamp] < #date

Answer 1

select s.*, u.timestamp
from stocks s
left join
(select su.stock_id, MAX(u.timestamp) timestamp
from updates u
inner join stock_updates su
on u.id = su.update_id
group by su.stock_id
) as u
on s.id = u.stock_id
where u.[timestamp] is null or u.[timestamp] < #date

Answer 2

Something like this perhaps?
SELECT s.*, v.timestamp
FROM stocks s
LEFT JOIN (
SELECT MAX(u.timestamp) AS timestamp, su.stock_id
FROM stock_updates su
INNER JOIN updates u ON (u.id = su.update_id)
GROUP BY su.stock_id
) v ON (v.stock_id = s.stock_id)
Basically it just joins the stocks table to an "inline view" that is the result of a query to determine the maximum timestamp for each stock_id.

Answer 3

I haven't included any filtering by the #date parameter, as your question states
"I'm trying to write a query that returns all the information about a
stock and the last time it was updated"
and for that you don't require any filtering.
This query does exactly that:
select s.*, dr.maxtime,
from stocks s
left join (select MAX(u.timestamp) as maxtime, su.stock_id
from stock_updates su inner join updates u on u.id = su.update_id
group by su.stock_id) dr
on dr.stock_id = s.stock_id
where
maxtime < #date or maxtime is null
[BTW: left join is the same as left outer join]

Answer 4

Try this
select s.*, max(su.timestamp)
from
stocks s
left outer join
stock_update su
on (s.id = su.stock_id)
left outer join
updates u
on (u.id = su.update_id)
group by s.*
It's written off the top of my head. What do you refer to with #date? Does that mean "now"? Do you mean the latest timestamp, or the latest before #date?