Sql 让子查询返回一行而不是一列

我有一个疑问：

SELECT 
    [Address]=e.Address, 
    [LastEmail] = 
    (
        SELECT TOP 1 [Email] 
        FROM Email innerE 
        WHERE e.UserID = innerE.UserID 
        AND innerE.Contact = @emailId
        AND (IsSent is null OR isSent = 0)
        ORDER BY Timestamp DESC
    )

FROM Emails e

这很好，但现在，我意识到我想得到包含最后一个电子邮件列的整行，如果可能的话，有什么办法吗？

您可以这样做：

;WITH LastEmails
AS
(
   SELECT *, 
     ROW_NUMBER() OVER(ORDER BY Timestamp DESC) rownum
   FROM Emails
   WHERE Contact = @emailId
     AND (IsSent is null OR isSent = 0)
)
SELECT * FROM LastEmails
WHERE rownum = 1;

---

如果您的DBMS支持它，您可以使用它（我认为它是这样的，因为它看起来像SQL Server语法）

---

这类似于相关子查询，但允许多行多列。

我使用了这个答案的组合，并提供了我所需要的。我也使用了rank（）代替row_number（）。

SELECT  [Address]=e.Address, 
        [LastEmail] = ie.Email
FROM    Emails e
        OUTER APPLY
        (   SELECT  TOP 1 *
            FROM    Email innerE 
            WHERE   e.UserID = innerE.UserID 
            AND     innerE.Contact = @emailId
            AND     (IsSent is null OR isSent = 0)
            ORDER BY Timestamp DESC
        ) ie