如何在Mysql计算中使用别名

Question

我通过计数操作创建了别名NumDrums。我想再次使用这个别名来创建另一个别名UnitTotal，一个计算列。当运行查询时，我得到以下错误：

执行查询时出错：#42S22不支持引用"NumDrums"(引用组功能(

Select
customers.CustCompanyName,
products.ProdUnNum,
customers.CustGenerator,
products.ProdID,
products.ProdSize,
products.ProdUnitName,
COUNT(*) as NumDrums,
(SELECT NumDrums) * products.ProdSize as UnitTotal

From
drums Inner Join
orders On drums.OrderID = orders.OrderID Inner Join
manifests On orders.ManifestID = manifests.ManifestID Inner Join
customers On drums.CustID = customers.CustID
And orders.CustID = customers.CustID Inner Join
products On drums.ProdID = products.ProdID
Group By
customers.CustCompanyName,products.ProdUnNum
Order by
customers.CustCompanyName

Answer 1

只需使用COUNT(*(*产品。ProdSize，感谢用户Thallius