SQL查詢使用列ALIAS

Question

這應該很容易，但我得到一個「無效列名稱」錯誤。

SELECT Transaction, COUNT(ItemId) AS ItemCount 
FROM TransactionTable 
WHERE ItemCount > 5 
GROUP BY Transaction 
ORDER BY ItemCount DESC 

這種說法作品，未經這似乎是雙重標準，對我來說，因爲ORDER BY使用列別名WHERE子句。

Answer 1

使用HAVING，並指定統計再次

SELECT Transaction, COUNT(ItemId) AS ItemCount 
FROM TransactionTable 
GROUP BY Transaction 
HAVING COUNT(ItemId) > 5 
ORDER BY ItemCount DESC 

原因ORDER BY正在與別名是因爲SQL查詢順序

處理FROM（包括聯接）
ON
OUTER
其中
GROUP BY
HAVING
SELECT
ORDER BY
TOP

Answer 2

SELECT [Transaction], COUNT(ItemId) AS ItemCount 
FROM TransactionTable 
WHERE ItemCount > 5 
GROUP BY COUNT(ItemId) 
ORDER BY COUNT(ItemId) DESC 

Answer 3

您可以參考列別名在ORDER BY如（邏輯）這是SELECT後處理。要使用WHERE或HAVING子句中的列別名，您可以在表格表達式中定義SELECT，例如，如下。

;WITH cte 
    AS (SELECT Transaction , 
       COUNT(itemid) AS itemcount 
     FROM transactiontable 
     GROUP BY Transaction) 
SELECT Transaction , 
     itemcount 
FROM transactiontable 
WHERE itemcount > 5 
ORDER BY itemcount DESC 

Answer 4

WITH tempTable AS 
(
    SELECT Transaction, COUNT(ItemId) AS ItemCount 
    FROM TransactionTable 
) 
SELECT * 
FROM tempTable 
WHERE ItemCount > 5 
GROUP BY Transaction 
ORDER BY ItemCount DESC