SQL结合两个查询

Question

下面的代码从两个表中选择记录，其中电子邮件和dob匹配另一个记录（所有重复。）

SELECT 
    AccountName, 
    EmailAddress, 
    DateOfBirth
FROM 
(
    SELECT 
        a.AccountName, 
        a.EmailAddress, 
        u.DateOfBirth, 
        COUNT(*) over (partition by a.EmailAddress, u.DateOfBirth) AS cnt
    FROM Account AS a 
    JOIN [User] AS u ON a.AccountID = u.AccountID              
) ua                
WHERE cnt > 1
AND EmailAddress IS NOT null
AND DateOfBirth IS NOT null     
ORDER BY EmailAddress, DateOfBirth 

我还想在此表中添加另一个名为“ Audit”的表中的字段。 我们可以使用LoginID加入他们，但是LoginID在Audit表中具有一对多的关系。 即，一个LoginID可以具有许多审核。

我要添加“审核开始日期”列。 以下查询使我可以按日期标识最新的审核。

         SELECT  a.LoginID as AuditLoginID,
         MAX(StartDate) as StartDate
         FROM    Audit as a
         GROUP BY  a.LoginID
         ORDER BY a.StartDate

谁能建议我如何组合这两个查询，以便我的原始查询具有到“审计”表的联接，并显示最新审计开始日期的“ StartDate”列？

Answer 1

您应该考虑使用相关子查询 。 这样可以避免构建另一个数据库对象来支持此查询，并且这是一个相对标准的SQL构造。

例：

SELECT 
    AccountName, 
    EmailAddress, 
    DateOfBirth
FROM 
(
    SELECT 
        a.AccountName, 
        a.EmailAddress, 
        u.DateOfBirth, 
        a.LoginID,
        COUNT(*) over (partition by a.EmailAddress, u.DateOfBirth) AS cnt
    FROM Account AS a 
    JOIN [User] AS u ON a.AccountID = u.AccountID              
) ua           
join Audit as a 
  on a.LoginID = au.LoginID     
WHERE cnt > 1
AND EmailAddress IS NOT null
AND DateOfBirth IS NOT null     
AND a.startdate = (SELECT MAX(StartDate) as StartDate
                   FROM    Audit as b
                   WHERE b.LoginID = a.LoginID)
ORDER BY EmailAddress, DateOfBirth 

Answer 2

这是我的评论的扩展：

CREATE VIEW MostRecentLogins AS
  (
     SELECT a.LoginID as AuditLoginID,
            MAX(StartDate) as StartDate
       FROM Audit as a
      GROUP BY a.LoginID
  )

然后，您可以将MostRecentLogins视图加入其他查询中。 从您的帖子中尚不清楚哪一列与LoginId对应（从Audit表中），但是查询看起来像这样：

SELECT a.AccountName, 
       a.EmailAddress, 
       u.DateOfBirth,
       MRL.StartDate
  FROM 
     (
       SELECT a.AccountName, 
              a.EmailAddress, 
              u.DateOfBirth, 
              COUNT(*) over (partition by a.EmailAddress, u.DateOfBirth) AS cnt
         FROM Account AS a 
              JOIN [User] AS u 
                       ON a.AccountID = u.AccountID              
     ) ua
     INNER JOIN MostRecentLogins MRL
         ON MRL.LoginID = a.LoginID    -- not sure what column should be on the RHS of this..
  WHERE cnt > 1
    AND EmailAddress IS NOT null
    AND DateOfBirth IS NOT null     
  ORDER BY EmailAddress, DateOfBirth