左外部加入选择前1个结果为空

Question

当我使用以下代码加入最近更新的地址时，它导致ZIP中的所有相关字段返回为NULL。我已经尝试了一个外部应用程序，它做得更好，但它不会从右侧的两个表中检索到每一个zip，即使它们存在。

SELECT 
    i.ion_ID as [ION], 
    zip.City as [City], 
    zip.StateCode as [State], 
    zip.ZipCode as [Zip Code], 
    zip.County as [County] 
FROM  
    HWSP_t_ION i 
     LEFT OUTER JOIN (SELECT TOP 1 ad.AssociatedIDValue, z.Zipcode, z.City, z.StateCode, z.County 
            FROM CADD_t_Address ad 
             LEFT OUTER JOIN CADD_lt_ZipCode z 
              ON ad.zip = z.ZipCode 
            ORDER BY ad.ChangedOn desc 
             ) AS ZIP 
     ON zip.AssociatedIDValue = i.ION_ID 

编辑： 这是外应用看起来像：

SELECT 
    i.ion_ID as [ION], 
    zip.City as [City], 
    zip.StateCode as [State], 
    zip.ZipCode as [Zip Code], 
    zip.County as [County] 
OUTER APPLY       (SELECT TOP 1 ad.zip 
            FROM CADD_t_Address ad 
            WHERE ad.AssociatedIDValue = ci.ION_ID 
            and [ad].[Status] = 'ACTIVE' 
            ORDER BY ad.ChangedOn desc 
             ) ad 


OUTER APPLY       (SELECT TOP 1 zip.Zipcode, zip.City, zip.StateCode, zip.County as [County] 
            FROM CADD_lt_ZipCode zip 
            WHERE ad.zip = zip.ZipCode 
            ) zip 

Answer 1

当使用SQL工作，内置认为你的数据。想想你想如何组合。在这种情况下，你只需要一行内部集合来获取外部集合的数据。窗口函数对于内部集合非常适用。您正在生成一个行号（rn）来指定排序中的第一行，然后排除任何不是rn = 1的行。一旦你有这个单一的最新记录，然后只是链接两套。

试着这么做：

SELECT 
    t1.ID 
    , s2.blah 
    , s2.moreBlah 
FROM t1 
LEFT OUTER JOIN (
    SELECT * 
    FROM (
     SELECT t2.id, t2.blah, t3.moreBlah 
      , ROW_NUMBER() OVER (PARTITION BY <columnToBaseOrderFrom> ORDER BY changeDate DESC) AS rn 
     FROM t2 
     LEFT OUTER JOIN t3 ON t2.refID = t3.id 
    ) s1 
    WHERE rn = 1 
) s2 ON t1.id2 = s2.id 

如果你需要消除NULL的记录，你必须确定，如果你想从T1到被淘汰的行，如果他们没有从比赛s2子查询。如果是这样的话，你需要INNER JOIN而不是LEFT OUTER JOIN。