@H_404_0@ 表/连接/一张表和另一张表的聚合字段连接

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@H_404_0@用Northwind中的表：

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SELECT CustomersID,CompanyName,ContactName,Address,
City,Region,Phone,a.orderCount
FROM dbo.CustomersInfo,(SELECT CustomerID,SUM(OrderAmount) AS orderCount FROM dbo.Orders GROUP BY CustomerID) as a
WHERE CustomersInfo.CustomersID=a.CustomerID

@H_404_0@主要把select的结果集重新命名a

@H_404_0@这样就可以调用a的字段了