Question

select campaign
,ISNULL(sum(cast (HandleTime as bigint)), 0) handleTime
,(select Contacts from [View_ContactsByCampaign] Con where Con.Campaign = C.Campaign) Contacts
, ContactPerTime = Contacts / handleTime
from call C
group by campaign

我在计算ContactPerTime值时遇到问题。我收到“无效的列名'联系人'。”和“无效的列名'handleTime'”错误。是否可以使用这些值进行计算？

Answer 1

您不能通过别名引用SELECT语句中的其他列。如果你再次需要表达式，你需要重复所述表达式：

SELECT campaign,
       ISNULL(SUM(CAST (HandleTime AS bigint)), 0) AS handleTime,
       (SELECT Contacts
        FROM [View_ContactsByCampaign] Con
        WHERE Con.Campaign = C.Campaign) AS Contacts,
       (SELECT Contacts
        FROM [View_ContactsByCampaign] Con
        WHERE Con.Campaign = C.Campaign) / handleTime AS ContactPerTime
FROM [CALL] C
GROUP BY campaign;

但是，正如您所拥有的是子查询，您最好使用APPLY。可能类似::

SELECT campaign,
       ISNULL(SUM(CAST (HandleTime AS bigint)), 0) AS handleTime,
       Con.Contacts
       Con.Contacts / handleTime AS ContactPerTime
FROM [CALL] C
     CROSS APPLY(SELECT Contacts
                 FROM [View_ContactsByCampaign] ca
                 WHERE ca.Campaign = C.Campaign) Con
--Considering that Contacts was returned from a subquery, it's likely a "safe"
--assumption it will return 1 row. If it didn't, then your previous query
--would have errored anyway.
GROUP BY campaign, Contacts;

供参考，请查看Logical Processing Order of the SELECT statement：其中说明：

相反，因为SELECT子句是步骤8，所以任何列别名或该子句中定义的派生列不能被引用前面的条款。但是，它们可以通过后续引用条款，例如ORDER BY子句。

ORDER BY实际上是唯一可以在语句的同一部分通过别名引用列的位置。

使用选定的值计算新值

1 个答案: