Question

如何将子查询的结果包含在WHERE子句中？

例如，我有以下声明（因为原文很大而减少）：

    SELECT   o.ID AS OrderSpecsID, o.CustomerID, o.EstimateNo, o.OrderYear,

        (SELECT  COUNT(*) 
                 FROM  OrderSpecs AS os 
                 WHERE (o.OrderID = OrderID)) AS AmendmentCount

         FROM  OrderSpecs AS o LEFT OUTER JOIN 
               Orders ON o.OrderID = Orders.ID

   WHERE (o.CustomerID = 30)

我想在我的WHERE子句中包含AmendmentCount字段，如下所示：

WHERE (o.CustomerID = 30) AND (AmendmentCount > 0)

但是，如果我设置上述内容，则会出现以下错误：

无效的列名'AmendmentCount'

如何将AmendmentCount字段用于我的WHERE子句？

非常感谢，

罗布

Answer 1

使用CTE或子查询：

with cte as (
      SELECT o.ID AS OrderSpecsID, o.CustomerID, o.EstimateNo, o.OrderYear,
             (SELECT  COUNT(*) 
                      FROM  OrderSpecs AS os 
                      WHERE (o.OrderID = OrderID)
             ) AS AmendmentCount
      FROM  OrderSpecs AS o LEFT OUTER JOIN 
            Orders
            ON o.OrderID = Orders.ID
    )
select *
from cte
where (CustomerID = 30) and (AmendmentCount > 0);

但是，如果你的情况，编写查询的更好方法可能是使用窗口函数：

select os.*
from (select os.ID AS OrderSpecsID, os.CustomerID, os.EstimateNo, os.OrderYear,
             count(o.OrderId) over (partition by os.OrderId) as AmendmentCount
      from OrderSpecs os left outer join
           Orders o
           on os.OrderID = o.ID
     ) os
where (CustomerID = 30) and (AmendmentCount > 0);

我有点不清楚CustomerId上的过滤器在这种情况下是否应该在子查询或外部查询中。一个或另一个应该适合你正在做的事情。

Answer 2

您可以在查询中添加带有联接的选择

FROM  OrderSpecs
join (SELECT  COUNT(*), OrderID  
             FROM  OrderSpecs AS os 
             WHERE (o.OrderID = OrderID)) AS Amendment on Amendment.OrderID = OrderSpecs.OrderID

SQL：如何在WHERE子句中包含SubQuery列结果？

2 个答案: