MYSQL: How to get the current entry of multipe tables - mysql

Question

I got three tables with data for products:
One where the products are defined.
A second where is defined which store has what products with what priceing with a timestamp.
And a third with the stock in the store of the products that are assiged.
Table 1 - products:
prdoductID|Name
----------|-------
1 |banana
2 |apple
Table 2 - prices:
storeID | productID | price | timestamp
--------|-----------|-------|------------
1 | 1 | 5,90 | 2016-03-27 16:00:00
1 | 1 | 5,90 | 2016-03-27 17:00:00
2 | 1 | 5,00 | 2016-03-27 16:00:00
2 | 2 | 5,00 | 2016-03-27 16:00:00
2 | 2 | 5,90 | 2016-03-28 19:00:00
Table 3 - stocks:
storeID | productID | stock | timestamp
--------|-----------|-------|------------
1 | 1 | 50 | 2016-03-27 08:00:00
1 | 1 | 5 | 2016-03-27 17:00:00
2 | 1 | 60 | 2016-03-27 09:00:00
2 | 2 | 0 | 2016-03-27 16:00:00
2 | 2 | 55 | 2016-03-28 19:00:00
`
Now I want to get the current state of one store for example at time 2016-03-27 14:00:00.
My current query get's for me the data but for all timestamps. I just want to get the corresponding entrys with the recent timesamps for each product of this store with the storeID = x;
Note: The user is able to plan. So there could be entries with futre timestamps so just a MAX would not work.
Query:
SELECT price.*, prod.name, stock.timestamp as 'stockTimesamp',
stock.stock FROM prices price
LEFT OUTER JOIN products prod on price.productID = prod.productID and
price.timestamp=(SELECT MAX(price.timestamp) WHERE price.timestamp <= '2016-03-27 14:00:00' and price.productID = prod.productID)
LEFT OUTER JOIN stocks stock on price.storeID = best.storeID and price.productID = stock.productID and stock.timestamp=(SELECT MAX(best.timestamp) WHERE stock.timestamp <= '2016-03-27 14:00:00' and stock.productID = prod.productID and stock.productID = price.productID)
where price.storeID=21
ORDER BY stock.timestamp DESC
Hope you can help me out...

Answer 1

This is a troublesome data structure for this type of query. You can get the most recent timestamp per product for each table and then join back to get additional information:
select p.*,
(select max(timestamp)
from stocks s
where s.storeid = $storeid and s.productid = p.productid and
s.timestamp <= '2016-03-27 14:00:00'
) as stock_timestamp,
(select max(timestamp)
from prices pr
where pr.storeid = $storeid and pr.productid = p.productid and
pr.timestamp <= '2016-03-27 14:00:00'
) as stock_timestamp
from products p;
Then, join back to the original tables to get additional information:
select p.*, s.*, pr.*
from (select p.*,
(select max(timestamp)
from stocks s
where s.storeid = $storeid and s.productid = p.productid and
s.timestamp <= '2016-03-27 14:00:00'
) as stock_timestamp,
(select max(timestamp)
from prices pr
where pr.storeid = $storeid and pr.productid = p.productid and
pr.timestamp <= '2016-03-27 14:00:00'
) as price_timestamp
from products p
) p left join
stocks s
on s.storeid = $storeid and s.productid = p.productid and
s.timestamp = p.stock_timestamp left join
prices pr
on pr.storeid = $storeid and pr.productid = p.productid and
pr.timestamp = p.price_timestamp ;
I should note that your problem would be relatively trivial if you had an effective and end date on each record. That is a better way to store a slowly changing dimension.