Joining 3 tables on a date criteria - sql

Question

I need help with this.
Tbl: WarehouseInventory
Date | DelRec | ProductId | Quantity
2015-09-10 | 110 | 1 | 100
2015-09-12 | 111 | 1 | 100
2015-09-12 | 111 | 2 | 200
2015-09-12 | 111 | 3 | 300
Tbl: Withdrawals
Date | ID | ProductId | Quantity | CustomerId
2015-09-11 | 1 | 1 | 400 | 2
2015-09-12 | 1 | 1 | 100 | 1
2015-09-12 | 2 | 2 | 200 | 1
2015-09-12 | 3 | 3 | 300 | 1
Tbl: Customers
Customer Id | Name
1 | Somebody
2 | Someone
The output should be like this
DelRec | Date Added | ProductId | Stocked | Withdrawn | Customer
110 | 2015-09-10 | 1 | 100 | 0 | NULL
0 | 2015-09-11 | 1 | 0 | 400 | Someone
111 | 2015-09-12 | 1 | 100 | 100 | Somebody
111 | 2015-09-12 | 2 | 200 | 200 | Somebody
111 | 2015-09-12 | 3 | 300 | 300 | Somebody
This is what I have come up so far and it's giving me a wrong output
select wi.DateAdded as 'Date Added', max(wi.DeliveryReceipt) as 'Delivery Receipt', wi.ProductId as 'Product',
max(isnull(wi.Quantity, 0)) as 'Stocked', max(isnull(w.Quantity, 0)) as 'Withdrawn', e.Customers as 'Customer'
from WarehouseInventory wi
cross join Withdrawals w
cross join Customer e
group by wi.DateAdded, wi.ProductId, e.Customers, wi.DeliveryReceipt, w.ProductId
Basically, I need to join the two tables on the date and product and if there is a null value in one of the tables, just make it 0. I appreciate your help.

Answer 1

You can use a FULL OUTER JOIN:
SELECT DelRec,
COALESCE(wi.[Date], wd.[Date]) AS Date_Added,
COALESCE(wi.ProductId, wd.ProductId) AS ProductId,
COALESCE(wi.Quantity, 0) AS Stocked,
COALESCE(wd.Quantity, 0) AS Withdrawn,
c.Name AS Customer
FROM WarehouseInventory AS wi
FULL OUTER JOIN Withdrawals AS wd
ON wi.[Date] = wd.[Date] AND wi.ProductId = wd.ProductId
LEFT JOIN Customers AS c ON c.[Customer Id] = wd.CustomerId
ORDER BY Date_Added

Answer 2

You have a few inconsistencies between your example table and your query, but here's the basic gist:
You want to FULL OUTER JOIN your Warehouse delivery (A) and Withdrawal (B) tables on both product and date
Make sure you coalesce(A, B) for both date and product
Sum the quantities from each table, then coalesce outside each aggregate to get zeros (since one column can be all nulls).
Here:
select
coalesce(wi.DateAdded, w.date) as 'Date Added',
max(wi.DeliveryReceipt) as 'Delivery Receipt',
coalesce(wi.ProductId, w.productId) as 'Product',
coalesce(sum(wi.Quantity), 0) as 'Stocked',
coalesce(sum(w.Quantity), 0) as 'Withdrawn',
e.name as 'Customer'
from WarehouseInventory wi
full outer join Withdrawals w on w.date = wi.dateadded and w.productId = wi.productId
left join Customer e on e.customerId = w.customerId
group by
coalesce(wi.DateAdded, w.date),
coalesce(wi.ProductId, w.productId),
e.name