SQL Server 2012 SSMS Intellisense在WHERE子句中说“无效的列名称”

Question

当我尝试在SSMS 2012 Express上执行以下脚本时：

SELECT ItemID, ItemPrice, DiscountAmount, Quantity, 
    ItemPrice * Quantity AS PriceTotal, 
    DiscountAmount * Quantity AS DiscountTotal, 
    Quantity * (ItemPrice - DiscountAmount) AS ItemTotal
FROM OrderItems
WHERE ItemTotal > 500
ORDER BY ItemTotal DESC

“Intellisense”在WHERE子句中引用“ItemTotal”和“仅在WHERE子句中”表示“无效列名称”。如果我注释掉或删除WHERE子句，即使在ORDER BY子句中也调用了“ItemTotal”，它也能正常工作。

请帮忙。

非常感谢。

Answer 1

这是因为WHERE和ORDER BY在执行期间的两个不同时间进行评估：

• WHERE ：首先评估此项，然后开始构建 SELECT 将显示的“表格”
• ORDER BY ：计算此“表格”后对此进行评估，以便按照您提到的列开始排序

别名（即 AS 子句后面的名称）是对此“表格”列的某种“重命名”，它将与 SELECT 一起显示。这意味着在计算 WHERE 子句时它们尚不存在。

ORDER BY 在构建table后发生，因此系统现在知道别名引用的列。

要做你想做的事，你必须写：

SELECT ItemID, ItemPrice, DiscountAmount, Quantity, 
       ItemPrice * Quantity AS PriceTotal, 
       DiscountAmount * Quantity AS DiscountTotal, 
       Quantity * (ItemPrice - DiscountAmount) AS ItemTotal
FROM OrderItems
WHERE Quantity * (ItemPrice - DiscountAmount) > 500 --here SQL doesn't know what "ItemTotal" is...
ORDER BY ItemTotal DESC -- but at this stage it does understand !

Answer 2

Select * from 
            ( SELECT ItemID, 
                     ItemPrice,
                     DiscountAmount,
                     Quantity, 
                     ItemPrice * Quantity AS PriceTotal, 
                     DiscountAmount * Quantity AS DiscountTotal, 
                     Quantity * (ItemPrice - DiscountAmount) AS ItemTotal
              FROM OrderItems
             ) as t
         WHERE ItemTotal > 500 
         ORDER BY ItemTotal DESC 

Sample Working Sql Fiddle

希望这有帮助

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