仅更新SQL Server中重复条目的第一条记录

Question

我需要帮助尝试更新具有多个重复记录的表，但我被卡住了。

我有此表，我需要使用im_cust9值更新alt_item_id1。

我用来从表中获得此结果的查询如下：

 SELECT  
     o.item_id, o.alt_item_id1, o.im_cust9, o.owner_id, o.if_updatestamp
 FROM 
     item_master o
 INNER JOIN
     (SELECT 
          alt_item_id1, COUNT(*) AS dupeCount
      FROM 
          item_master 
      WHERE 
          owner_id = 'GIII' AND alt_item_id1 <> ''
      GROUP BY 
          alt_item_id1  
      HAVING 
          COUNT(*) > 1) oc ON o.alt_item_id1 = oc.alt_item_id1 
WHERE 
    owner_id = 'GIII' AND o.alt_item_id1 <> '' 
ORDER BY 
    alt_item_id1, if_updatestamp ASC

不确定如何更新每组重复的最旧记录alt_item_id1

我正在使用SQL Server 2012

非常感谢任何帮助！

Answer 1

要获取要更新的最新行，请使用 if_updatestamp 的最大值。对于最古老的使用最小。然后将它连接到你的表中为udpate这样......

update IM
Set IM.im_cust9 = NewDupeRow.alt_item_id1
From item_master IM
JOIN ( 
SELECT alt_item_id1,Max(if_updatestamp) MaxUpdateValue
 FROM item_master WHERE owner_id='GIII' AND alt_item_id1<>''
 GROUP BY alt_item_id1 ) NewDupeRow
 On IM.alt_item_ID = NewDupeRow.alt_item_ID
 AND IM.if_updatedstamp = NewDupeRow.MaxUpdateValue

Answer 2

您可以使用可更新的CTE和row_number()：

来执行此操作

with toupdate as (
      select i.*,
             row_number() over (partition by alt_item_id order by if_updatestamp) as seqnum
      from item_master i
     )
update toupdate
    set im_cust9 = alt_item_id1
    where seqnum = 1;