Question

我有这个查询：

select 
    *
    ,(select location from [order] where [id] = oi.OrderID) as orderlocation
    ,case 
        when oi.location is not null then oi.location
        when oi.location is null then orderlocation
        end
from
    orderitem oi

我得到一个错误：

无效的列名'orderlocation'

以下查询可以正常工作，并且可以完成预期的工作：

select  
    *
    ,(select location from [order] where [id] = oi.OrderID) as orderlocation
    ,case 
        when oi.location is not null then oi.location
        when oi.location is null then (select location from [order] where [id] = oi.OrderID)
        end
from
    orderitem oi

实际上，这不是一个巨大的问题，但是必须重复两次相同的文本，并且要记住，如果它改变了，则必须记住在两个地方都进行更新，这有点麻烦。有没有更好的方式来编写此查询，以便没有重复？也许使用变量之类的东西？我不是SQL专家，所以我不确定写这个的更好方法。

任何帮助将不胜感激。预先感谢！

Answer 1

您可以将子查询移至FROM：

select *, --This should really be a proper list
       ISNULL(oi.location,ol.orderlocation) AS OrderLocation2 --ISNULKL or COALESCE are much more succinct
from orderitem oi
     CROSS APPLY (select location AS orderlocation from [order] o where o.[id] = oi.OrderID)) o; --Use OUTER APPLY if this may not return a result

尽管查看您的代码，但这不是真的吗：

SELECT oi.*, --still should be a distinct column list
       o.location,
       ISNULL(oi.location,o.location ) AS OrderLocation
FROM dbo.orderitem oi
     JOIN dbo.[order] O ON o.[id] = oi.OrderIDl --LEFT JOIN if there may not be a row here.

Answer 2

扩展@John Cappelletti的评论。

select *
    ,ord.location  as orderlocation
    ,case 
        when oi.location is not null then oi.location
        when oi.location is null then ord.location
        end
from orderitem oi
LEFT JOIN [order] ORD on ord.[id] = oi.OrderID

Answer 3

我实际上已经在使用联接，但是我简化了该问题的查询。带有case语句的原始查询为

select * from orderitem oi inner join [order] o on oi.orderid = o.id

但是，我不知道合并或isull命令。他们工作得很好。我结束了：

select *
   ,coalesce(oi.location, o.location) as ManufacturingLocation
from orderitem oi inner join [order] o
on oi.orderid = o.id

感谢您的帮助！

在select语句的WHERE子句中使用动态列

3 个答案: