CTE后按最大列值的Sql分組

Question

我有這個查詢：

WITH messages_ranked 
AS ( 
   SELECT p.Date, p.RecipientId, p.RecipientType, p.Id, p.text, p.userId,
   ROW_NUMBER() OVER(PARTITION BY p.RecipientId, p.userId 
   ORDER BY p.Id DESC) 
   AS rk 

   FROM ChatMessages p
   JOIN ChatGroupMemberships as g 
   ON p.recipientId = g.groupId
   WHERE g.userId = XXX <-- user id
) 

SELECT date, recipientId as groupId, recipientType as groupType, id, text, userId, rk
FROM messages_ranked s 
where rk = 1

Order BY s.date DESC 

這給我帶來了這個：

我需要的是減少此查詢的結果行，以便對於每個唯一的groupId僅返回具有最高date值的行。

因此，例如從前三行只返回第一行，因為它們共享相同的groupId並且第一行具有最新日期。

我試圖在這里遵循示例如何通過 SQL 中的另一列選擇具有 MAX(Column value), DISTINCT 的行？ 因為我的問題密切相關，但我似乎做對了。

Answer 1

我猜這可以滿足您的需求：

WITH messages_ranked AS ( 
      SELECT p.Date, p.RecipientId, p.RecipientType, p.Id, p.text, p.userId,
             ROW_NUMBER() OVER (PARTITION BY p.RecipientId ORDER BY p.dATE DESC) AS seqnum
      FROM ChatMessages p JOIN
           ChatGroupMemberships as g 
           ON p.recipientId = g.groupId
      WHERE g.userId = XXX <-- user id
     ) 
SELECT date, recipientId as groupId, recipientType as groupType, id, text, 
       userId, seqnum
FROM messages_ranked s 
WHERE seqnum = 1
ORDER BY s.date DESC ;

我認為您不需要使用row_number()兩次。