比較兩個表其中一個分組

Question

我有2個表，需要加以比較：

TABLE 'orders' 
customer|product |colour|order_quantity 
Germany |product1|black |100 
Germany |product1|red |200 
Germany |product3|yellow|150 
UK  |product1|black |450 
UK  |product2|green |350 
UK  |product5|grey |100 
Italy |product1|grey |200 
Italy |product2|black |300 
Italy |product3|yellow|400 
Italy |product3|black |800 
Italy |product4|blue |250 
Italy |product5|grey |370 

TABLE 'inventory' 
product |colour|inventory_quantity 
product1|black |830 
product1|red |250 
product1|grey |600 
product1|mango |120 
product2|green |50 
product2|black |350 
product3|yellow|900 
product3|black |900 
product4|blue |210 
product4|black |50 
product4|green |25 
product5|grey |700 


Output wanted: 
product |colour|order_quantity|inventory_quantity|difference 
product1|black |550   |830    |180 
product1|red |200   |250    |50 
product1|grey |200   |600    |400 
product1|mango |0    |120    |120 
product2|green |350   |50    |-300 
product2|black |300   |350    |50 
product3|yellow|550   |900    |350 
product3|black |800   |900    |100 
product4|blue |250   |210    |-40 
product4|black |0    |50    |50 
product4|green |0    |25    |25 
product5|grey |370   |700    |330 

不過，目前我正在清點數量的倍數給我一個不正確的差異。如何比較'訂單'中的數量（按產品分組）和「庫存」（未分組）中的數量？

感謝， 德里克

Answer 1

這裏有一個選項

Select product, colour, order_Quantity, 
    Inventory_Quantity, Inventory_Quantity-Order_Quantity as difference 
FROM ORDERS I 
FULL OUTER 
(SELECT Sum(Order_Quantity), product, Colour 
FROM Inventory 
GROUP BY product, Colour) as O 
ON O.Product=I.Product 
and O.Colour = I.Colour 

第二個選項遵循：

Select product, colour, sum(order_Quantity), max(Inventory_Quantity), sum(order_Quantity)-max(inventory_Quantity) 
FROM Inventory I 
FULL OUTER JOIN O 
ON I.Product=O.Product 
and O.Colour = I.Colour 
GROUP BY product, colour 

選項3

SELECT product, colour, OQ as Order_Quantity, Inventory_Quantity, Inventory_Quantity-OQ as Difference 
    Select product, colour, sum(order_Quantity) as OQ , Inventory_Quantity 
    FROM Inventory I 
    FULL OUTER JOIN O 
    ON I.Product=O.Product 
    and O.Colour = I.Colour 
GROUP BY product, colour) 

使用全外連接，因爲訂單或庫存可能爲空，並懷疑您仍然希望有所不同。