Sum data from two tables with different number of rows - sql

Question

There are 3 Tables (SorMaster, SorDetail, and InvWarehouse):
SorMaster:
+------------+
| SalesOrder |
+------------+
| 100 |
| 101 |
| 102 |
+------------+
SorDetail:
+------------+------------+---------------+
| SalesOrder | MStockCode | MBackOrderQty |
+------------+------------+---------------+
| 100 | PN-1 | 4 |
| 100 | PN-2 | 9 |
| 100 | PN-3 | 1 |
| 100 | PN-4 | 6 |
| 101 | PN-1 | 6 |
| 101 | PN-3 | 2 |
| 102 | PN-2 | 19 |
| 102 | PN-3 | 14 |
| 102 | PN-4 | 6 |
| 102 | PN-5 | 4 |
+------------+------------+---------------+
InvWarehouse:
+------------+-----------+-----------+
| MStockCode | Warehouse | QtyOnHand |
+------------+-----------+-----------+
| PN-1 | A | 1 |
| PN-2 | B | 9 |
| PN-3 | A | 0 |
| PN-4 | B | 1 |
| PN-1 | A | 0 |
| PN-3 | B | 5 |
| PN-2 | A | 9 |
| PN-3 | B | 4 |
| PN-4 | A | 6 |
| PN-5 | B | 0 |
+------------+-----------+-----------+
Desired Results:
+------------+-----------------+--------------+
| MStockCode | SumBackOrderQty | SumQtyOnHand |
+------------+-----------------+--------------+
| PN-1 | 10 | 10 |
| PN-2 | 28 | 1 |
| PN-3 | 17 | 5 |
| PN-4 | 12 | 13 |
| PN-5 | 11 | 6 |
+------------+-----------------+--------------+
I have been going around in circles with no end in sight. Seems like it should be simple but just can't wrap my head around it. The SumBackOrderQty obviously getting counted twice as the SumQtyOnHand is evaluated. To this point I have been doing the calculations in the PHP instead of the select statement but would like to clean things up a bit where possible.
Current query statement is:
SELECT SorDetail.MStockCode,
SUM(SorDetail.MBackOrderQty) AS 'SumMBackOrderQty',
SUM(InvWarehouse.QtyOnHand) AS 'SumQtyOnHand'
FROM SysproCompanyJ.dbo.SorMaster SorMaster,
SysproCompanyJ.dbo.SorDetail SorDetail LEFT OUTER JOIN SysproCompanyJ.dbo.InvWarehouse InvWarehouse
ON SorDetail.MStockCode = InvWarehouse.StockCode
WHERE SorMaster.SalesOrder = SorDetail.SalesOrder
AND SorMaster.ActiveFlag != 'N'
AND SorDetail.MBackOrderQty > '0'
AND SorDetail.MPrice > '0'
GROUP BY SorDetail.MStockCode
ORDER BY SorDetail.MStockCode ASC

Answer 1

Without providing the complete picture, in terms of your RDBMS, database schema, a description of the problem you're trying to solve and sample data that matches the aforementioned, the following is just an illustration of what a solution based on Barmar's comment could look like:
SELECT SD.MStockCode,
SD.SumBackOrderQty,
IW.SumQtyOnHand
FROM (SELECT MStockCode,
SUM(MBackOrderQty) AS `SumBackOrderQty`
FROM SorDetail
JOIN SorMaster ON SorDetail.SalesOrder=SorMaster.SalesOrder
WHERE SorMaster.ActiveFlag != 'N'
AND SorDetail.MBackOrderQty > 0
AND SorDetail.MPrice > 0
GROUP BY MStockCode) AS SD
LEFT JOIN (SELECT MStockCode,
SUM(QtyOnHand) AS `SumQtyOnHand`
FROM InvWarehouse
GROUP BY MStockCode) AS IW ON SD.MStockCode=IW.MStockCode
ORDER BY SD.MStockCode;

Answer 2

Here's one approach:
select MStockCode,
(select sum(MBackOrderQty) from sorDetail as T2
where T2.MStockCode = T1.MStockCode ) as SumBackOrderQty,
(select sum(QtyOnHand) from invWarehouse as T3
where T3.MStockCode = T1.MStockCode ) as SumQtyOnHand
from
(
select mstockcode from sorDetail
union
select mstockcode from invWarehouse
) as T1
In a fiddle here: http://sqlfiddle.com/#!9/fdaca/6
Though my SumQtyOnHand values don't match yours (as #Gordon pointed out).