CTE后按最大列值分组的Sql

Question

我有这个问题：

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 

这给了我这个：

我需要减少此查询的结果行，以便对于每个唯一的 groupId，只返回最高值为 date 的行。

例如，前三行仅返回第一行，因为它们共享相同的groupId，并且第一行具有最新的日期。

我尝试在How can I SELECT rows with MAX(Column value), DISTINCT by another column in SQL? 处遵循示例，因为我的问题密切相关，但我似乎做错了。

Answer 1

我猜这是你想要的：

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 ;

我认为您不需要使用两次row_number()。