SUM（）的多個值相關表

Question

我有一個MySQL數據庫三個相關表：

• inventory_items定義倉庫物品的種類
• inventory_transactions定義廣告的添加或刪除
數量
• 的位置上確定的位置說庫存

Inventory_transactions有許多存儲在給定inventory_item如何添加或刪除一個quantity_offset從給定的位置。

我有以下查詢，它將獲得global_quantity（給定inventory_item_id的所有quantity_offsets的總和）以及location_quantity，只要知道位置ID，它就可以爲特定位置執行相同的操作。

SELECT sku, name, SUM(quantity_offset) AS global_quantity, 
(
SELECT SUM(quantity_offset) 
    FROM inventory_transactions 
    WHERE inventory_items.inventory_item_id = inventory_transactions.inventory_item_id AND inventory_transactions.location_id = 1 
) AS location_quantity 
FROM inventory_items 
JOIN inventory_transactions ON inventory_items.inventory_item_id = inventory_transactions.inventory_item_id 
GROUP BY sku 

我想用被添加到每個位置的列結束了，所以結果可能有值，例如：

sku, name, global_quantity, denver_quantity, dallas_quantity, ft_wayne_quantity 

我的回退是要做到這一點對個人inventory_item頁面（當我就知道庫存物品，可以通過定位組），但能做到在一個單一的查詢，並把它全部納入一個表將是非常巨大的。

起初，我以爲我可以通過迭代子查詢，但無法設置列名（AS）編程。

非常感謝您提供任何幫助。

Answer 1

順便說一句，而不是使用子查詢SELECT列表中，你可以得到與上如果行是從給定的位置，有條件地返回quantity_offset的計算式的SUM聚合相同的結果。我也將使用左外連接到inventory_transactions表，這樣我就一定要得到一個回行的每一行中inventory_items：

SELECT i.sku 
    , i.name 
    , SUM(t.quantity_offset) AS global_quantity 
    , SUM(IF(t.location_id = 1,t.quantity_offset,NULL)) AS location_1_quantity 
    FROM inventory_items i 
    LEFT 
    JOIN inventory_transactions t ON i.inventory_item_id = t.inventory_item_id 
    GROUP BY i.sku 

（這不回答你的問題，但我想讓你意識到這一點）。

要回答你的問題，首先，SELECT語句無法動態地改變它在結果集中返回的列的數量或類型。你需要定義你想返回的每一列的表達式。 （在SQL SELECT statment文字的產生可動態完成，產生特定的SELECT語句，而是由SELECT語句返回的列由SELECT語句固定。）

如果我有一個相對固定的LOCATION_ID價值觀，我需要的結果集指定，我會重複的條件表達式多次的總和，每進行一次位置或什麼的，我想位置設置：

SELECT i.sku 
    , i.name 
    , SUM(t.quantity_offset) AS global_quantity 
    , SUM(IF(t.location_id = 1,t.quantity_offset,NULL)) AS location_1_quantity 
    , SUM(IF(t.location_id = 2,t.quantity_offset,NULL)) AS location_2_quantity 
    , SUM(IF(t.location_id = 3,t.quantity_offset,NULL)) AS location_3_quantity 
    , SUM(IF(t.location_id IN (1,2,3),t.quantity_offset,NULL)) AS location_123_quantity 
    , SUM(IF(t.location_id = 4,t.quantity_offset,NULL)) AS location_4_quantity 
    FROM inventory_items i 
    LEFT 
    JOIN inventory_transactions t ON i.inventory_item_id = t.inventory_item_id 
    GROUP BY i.sku 

如果要返回的列的集合需要真正動態，那麼我不會將它們作爲列返回。相反，我會將每個位置的SUM（quantity_offset）作爲單獨的行返回，然後在客戶端處理轉換爲列式表示。

Answer 2

試試這個

SELECT sku, name, SUM(quantity_offset) AS global_quantity, 
     (
     SELECT SUM(quantity_offset) 
     FROM inventory_transactions 
      WHERE inventory_items.inventory_item_id = inventory_transactions.inventory_item_id AND inventory_transactions.location_id = 1 
      AND location = denver) AS denver_quantity , 
     (
     SELECT SUM(quantity_offset) 
     FROM inventory_transactions 
      WHERE inventory_items.inventory_item_id = inventory_transactions.inventory_item_id AND inventory_transactions.location_id = 1 
      AND location = dallas) AS dallas_quantity, 
     (
     SELECT SUM(quantity_offset) 
     FROM inventory_transactions 
      WHERE inventory_items.inventory_item_id = inventory_transactions.inventory_item_id AND inventory_transactions.location_id = 1 
      AND location = ft_wayne) AS ft_wayne_quantity 
    FROM inventory_items 
    JOIN inventory_transactions ON inventory_items.inventory_item_id = inventory_transactions.inventory_item_id 
    GROUP BY sku 

注意我用了location作爲列名我不知道你有什麼位置的列名，只是更換

Answer 3

您應該使用有條件的資金 - 這是最有效的方式（最快的查詢）我知道的：

SELECT sku, name, SUM(quantity_offset) AS global_quantity, 
    sum(case when inventory_transactions.location_id = 1 then quantity_offset else 0 end) as loc1_quantitity, 
    sum(case when inventory_transactions.location_id = 2 then quantity_offset else 0 end) as loc2_quantitity, 
    sum(case when inventory_transactions.location_id = 3 then quantity_offset else 0 end) as loc3_quantitity 
FROM inventory_items JOIN inventory_transactions ON inventory_items.inventory_item_id = inventory_transactions.inventory_item_id 
GROUP BY sku