Question

我有一个数据库表a（EMAILS），其中EmailID是主键

EmailID     Email_To     Email_From    Email_Subject    Email_Registered    Email_Read

如果用户创建了一封电子邮件，则会在此表中注册。

例如，用户＆＃34; Dave＆＃34;谁拥有身份3发送电子邮件给＆＃34;约翰＆＃34;谁有id 4

所以这会给出

EmailID     Email_To     Email_From    Email_Subject    Email_Registered    Email_Read
   10          4             3              TEST        2/23/2016 11:00       False

要返回结果，我选择（加入用户个人资料数据库）

SELECT PROFILE_1.SellerID, PROFILE_1.Seller_UserName, EMAILS.EmailID, EMAILS.Email_From, EMAILS.Email_To, EMAILS.Email_Subject, 
                  EMAILS.Email_Registered, EMAILS.Email_Read,
                      (SELECT Seller_UserName AS Epr2
                        FROM PROFILE
                        WHERE (SellerID = EMAILS.Email_To)) AS Expr2
FROM PROFILE AS PROFILE_1 LEFT OUTER JOIN
                  EMAILS ON EMAILS.Email_From = PROFILE_1.SellerID
WHERE (EMAILS.Email_From IS NOT NULL) AND (PROFILE_1.Seller_UserName = 'Dave')
ORDER BY EMAILS.Email_Registered DESC

John回复Dave的电子邮件，然后进入EMAILS_THREAD表并注册为

EmailThreadID     EmailID     Email_To     Email_From     Email_Registered     Email_Read
      1              10          3             4           2/23/2016 11:05       False

我要做的是选择

来自EMAILS的选项，其中Email_From来自Dave，并在结果中返回EMAIL_THREADS发送给Dave的前1个结果（基于Email_Registered），如果EMAIL_THREADS中有条目，则使用与EMAILS.EmailID相同的EmailID。 / p>

换句话说，如果有的话，返回EMAIL表的结果和EMAIL_THREADS表中的最新相应结果。

我希望这是有道理的。

我尝试了很多组合，我无法解决这个问题。

起初我认为这是一个子查询，或者是一个联合或一组...但我似乎无法确定选择及其结构。

寻求帮助。

这是我的最后一次尝试

SELECT PROFILE_1.SellerID, PROFILE_1.Seller_UserName, EMAILS.EmailID, EMAILS.Email_From, EMAILS.Email_To, EMAILS.Email_Subject, 
                 EMAILS.Email_Registered, EMAILS.Email_Read,
                      (SELECT Seller_UserName AS Epr2
                        FROM PROFILE
                        WHERE (SellerID = EMAILS.Email_To)) AS Expr2
FROM PROFILE AS PROFILE_1 LEFT OUTER JOIN
                  EMAILS ON EMAILS.Email_From = PROFILE_1.SellerID CROSS JOIN
                      (SELECT TOP (1) EMAILS_THREAD.Email_From, EMAILS_THREAD.Email_To, EMAILS_THREAD.Email_Registered, EMAILS_THREAD.Email_Read
                        FROM EMAILS_THREAD LEFT OUTER JOIN
                                               EMAILS AS EMAILS_1 ON EMAILS_THREAD.EmailID = EMAILS_1.EmailID) AS derivedtbl_1
WHERE (EMAILS.Email_From IS NOT NULL) AND (PROFILE_1.Seller_UserName = 'Dave')
ORDER BY EMAILS.Email_Registered DESC

但它根本没有从EMAILS_THREADS返回任何内容。

Answer 1

来自EMAILS的选项，其中Email_From来自Dave，并在结果中返回EMAIL_THREADS的前1个结果，该结果发送给Dave（基于Email_Registered），如果EMAIL_THREADS.Hope中有条目，则使用与EMAILS.EmailID相同的EmailID这有帮助

   with cte
as
(select
* from emails 
where email_from=3
)
select * from cte mt --only for dave
outer apply
(
select top 1* from 
emial_threads st where mt.mail_from=st.mail_to ---send to dave
and mt.emailid=st.emailid) b

Answer 2

未能找到解决方案，所以我付钱给SQL专业人员为我解决这个问题。感谢Tab和The Gameiswar的输入。非常感谢。

SQL 2005使用子查询返回唯一结果

2 个答案: