創建一個能夠找出服裝物品價格超過50美元的查詢

Question

我需要幫助，我可以創建一個qquery來查找哪個服裝類別的銷售額超過50美元。
到目前爲止，我寫了這個：

SELECT 
ITEM_TYPE.Description AS [Item Type Name], 
ITEM.ItemID * price AS [Total Spent] 
FROM ITEM 
INNER JOIN ITEM_TYPE ON ITEM.ItemTypeID = ITEM_TYPE.ItemTypeID 
INNER JOIN ORDER_ITEM ON ITEM.ItemID = ORDER_ITEM.ItemID 
where ITEM_TYPE.Description Like '%Ladies%' 

但輸出只能顯示1行「衣夫人」，銷量的80.50

Answer 1

一個總我想你想一個GROUP BY子句和聚合函數SUM() ：

SELECT 
ITEM_TYPE.Description AS [Item Type Name], 
SUM(price) AS [Total Spent] -- ### apply SUM() 
FROM ITEM 
INNER JOIN ITEM_TYPE ON ITEM.ItemTypeID = ITEM_TYPE.ItemTypeID 
INNER JOIN ORDER_ITEM ON ITEM.ItemID = ORDER_ITEM.ItemID 
where ITEM_TYPE.Description Like '%Ladies%' 
GROUP BY ITEM_TYPE.Description -- ### add grouping for SUM() 

我懷疑你想多項price項目的ID。如果price爲訂單項的總計價格，那麼上面只是SUM(price)。如果price是商品價格，那麼您可能需要諸如SUM(price * quantity)之類的商品。

如果需要的總四捨五入到小數點後2位，使用ROUND：

ROUND(SUM(ITEM.ItemID * price), 2) AS [Total Spent] -- ### apply ROUND() 

Answer 2

你會做的總和，這是一個聚集。在應用聚合時，您必須按任何非聚合列進行分組。要對集合進行過濾，請使用HAVING指定SELECT的條件。例如：

SELECT 
ITEM_TYPE.Description AS [Item Type Name], 
SUM(ITEM.ItemID * price) AS [Total Spent] --aggregate column 
FROM ITEM 
INNER JOIN ITEM_TYPE ON ITEM.ItemTypeID = ITEM_TYPE.ItemTypeID 
INNER JOIN ORDER_ITEM ON ITEM.ItemID = ORDER_ITEM.ItemID 
where ITEM_TYPE.Description Like '%Ladies%' 
GROUP BY ITEM_TYPE.Description  --GROUP BY the non aggregate columns 
HAVING SUM(ITEM.ItemID * price) > 50 --HAVING filters the aggregate column 

Answer 3

，你必須使用GROUP BY和HAVING條款。 GROUP BY爲組相同的描述中的所有行在一起，HAVING的價格之和過濾超過50

SELECT 
    ITEM_TYPE.Description AS [Item Type Name], 
    SUM(ITEM.ItemID * price) AS [Total Spent] 
FROM ITEM 
    INNER JOIN ITEM_TYPE ON ITEM.ItemTypeID = ITEM_TYPE.ItemTypeID 
    INNER JOIN ORDER_ITEM ON ITEM.ItemID = ORDER_ITEM.ItemID 
WHERE ITEM_TYPE.Description Like '%Ladies%' 
GROUP BY ITEM_TYPE.Description  
HAVING SUM(ITEM.ItemID * price) > 50 

由子句你願意瞭解更多關於他們https://www.w3schools.com/sql/sql_having.asp