SQL Server Rank() by date, Group and Join 两个表，包括分页

Question

在 SQL Server 中有这两个表：

购物车：

id    userid    prodid    qt    date
1     21        P1        1     2017-02-18
2     21        P8        1     2017-02-19
3     21        P2        1     2017-02-20
4     22        P5        1     2017-02-21
5     22        P3        1     2017-02-22
6     23        P4        1     2017-02-23

用户：

id    user_name
21    John
22    James
23    Alice
24    Lily

我想要一个表，其中仅显示具有最新日期的 文章，按 user_id 分组，有 1 列 (art_c)，其中包含每个用户添加到购物车的文章数（不是 Qt，即数量)，并加入了 Users 表。 另外，我想为每一行结果添加分页。

我想要的结果是这样的：

id    userid    user_name    prodid   art_c   date
3     21        John         P2       3       2017-02-20
5     22        James        P3       2       2017-02-22
6     23        Alice        P4       1       2017-02-23

最好/最快的方法是什么？ 我正在使用这个请求，但我不确定它是否是好/快的方法：

With tb_a as 
(
  SELECT u_id,u_name,dat,art_c,ROW_NUMBER() OVER (ORDER BY u_name) as rgw FROM
  shopcart a
  LEFT JOIN 
  (SELECT 
       a.userid as u_id,
       b.user_name as u_name,
       Format(shop_date, 'dd.MM.yyyy HH:mm') as dat,
       RANK() OVER (PARTITION BY a.userid ORDER BY shop_date DESC) as dest_rank,
       Count(a.id) OVER (PARTITION BY a.userid ORDER BY shop_date) as art_c
       FROM 
            shopcart a
       LEFT JOIN 
            Users b on a.userid=b.id
  group by 
       a.userid,b.name,shop_date,a.id) b on a.userid=b.u_id 
  where dest_rank = 1
  group by u_id,u_name,dat,art_c
)

SELECT * FROM tb_a
WHERE rgw BETWEEN 0 AND 100 order by rgw

Answer 1

我认为你只需要在ShopCart 上使用row_number()。我会在join 之前这样做：

select u.*, sc.*
from (select sc.*,
             row_number() over (partition by sc.userid order by date desc) as seqnum
      from ShopCart sc
     ) sc join
     users u
     on sc.userid = u.id
where seqnum = 1;

对于分页，您可以添加order by，然后您可以使用offset 和fetch next。

编辑：

您也可以使用窗口函数获取计数：

select u.*, sc.*
from (select sc.*,
             row_number() over (partition by sc.userid order by date desc) as seqnum,
             count(*) over (partition by sc.userid) as cnt
      from ShopCart sc
     ) sc join
     users u
     on sc.userid = u.id
where seqnum = 1;

Answer 2

使用 with 语句和 Row_Number 如下，PartNo 列将按 userId 和 SeqNo 列对您的数据进行分组，以获得用户明智的计数：

;WITH S AS
(
    SELECT 
        *,
        COUNT(Id) OVER (PARTITION BY UserId) AS PartNo,
        ROW_NUMBER() OVER (PARTITION BY UserId Order BY Date DESC) AS SeqNo
    FROM @ShopCart SC
)

SELECT
    S.Id,
    S.UserId,
    U.UserName  ,
    S.ProdId,
    S.PartNo AS Art_c,
    S.Date
FROM S
LEFT JOIN @User U ON S.UserId=U.Id
WHERE S.SeqNo=1

Answer 3

;WITH Shopcart (id,userid,prodid,qt,date)
As
(
Select 1, 21,'P1',1, '2017-02-18' Union all
Select 2, 21,'P8',1, '2017-02-19' Union all
Select 3, 21,'P2',1, '2017-02-20' Union all
Select 4, 22,'P5',1, '2017-02-21' Union all
Select 5, 22,'P3',1, '2017-02-22' Union all
Select 6, 23,'P4',1, '2017-02-23'
)
,Users(id,[user_name])
As
(
Select 21,'John'  Union all
Select 22,'James' Union all
Select 23,'Alice' Union all
Select 24,'Lily'
)

,cte_result AS (
        SELECT c.id
            ,c.userid
            ,u.[user_name]
            ,c.prodid
            ,c.[date]
            ,COUNT(qt) OVER (PARTITION BY userid,[user_name]) art_c
            ,Row_number() OVER (PARTITION BY [user_name] ORDER BY [user_name],[date] DESC   ) Seq
        FROM Shopcart c
        INNER JOIN Users u ON u.id = c.userid
        )


SELECT id
    ,userid
    ,[user_name]
    ,prodid
    ,art_c
    ,[date]
FROM cte_result
WHERE Seq = 1
ORDER BY 1