限制加入的结果答案

【问题标题】：Limit results in join限制加入的结果
【发布时间】：2014-05-03 01:25:51
【问题描述】：

两张桌子。一个包含项目列表，另一个包含项目的阶段。我需要展示项目的最新阶段。我目前拥有的 SQL 显示了所有阶段，看起来像这样：

SELECT
    a.proj_name,
    a.proj_phase,
    c.proj_actions_next_action,
    c.proj_actions_next_action_date
FROM
    projects a  
LEFT OUTER JOIN
    Projects_actions c
        ON a.proj_id = c.proj_actions_projects_link
LEFT OUTER JOIN
    Clients b
        ON a.proj_clientlink = b.client_id
ORDER BY b.clientname

输出看起来像这样：

proj_name | proj_phase | proj_actions_next_action | proj_actions_next_action_date
Denmark   | Active     | Call X person            | 1/1/2014
Denmark   | Active     | Call Y person            | 2/1/2014
Denmark   | Active     | Do this presentation     | 3/1/2014
Denmark   | Active     | Sell this product        | 4/1/2014
UK Asset  | Active     | Call Y person            | 1/2/2014
UK Asset  | Active     | Call X person            | 1/3/2014
UK Asset  | Active     | Call Y person            | 2/4/2014
UK Asset  | Active     | Do this presentation     | 3/5/2014
UK Asset  | Active     | Sell this product        | 4/6/2014

我希望它看起来像这样：（仅显示最新的 proj_actions_next_action_date）

proj_name | proj_phase | proj_actions_next_action | proj_actions_next_action_date
Denmark   | Active     | Sell this product        | 4/1/2014
UK Asset  | Active     | Sell this product        | 4/6/2014

谢谢大家！

【问题讨论】：

只要得到最大（日期）。

标签： sql sql-server tsql join outer-join

【解决方案1】：

SELECT  Q.proj_name,
        Q.proj_phase,
        Q.proj_actions_next_action,
        Q.proj_actions_next_action_date
FROM (
SELECT
    a.proj_name,
    a.proj_phase,
    c.proj_actions_next_action,
    c.proj_actions_next_action_date,
    ROW_NUMBER() OVER (PARTITION BY a.proj_name 
           ORDER BY c.proj_actions_next_action_date DESC) AS RN
    ,b.clientname

FROM
    projects a  
LEFT OUTER JOIN
    Projects_actions c
        ON a.proj_id = c.proj_actions_projects_link
LEFT OUTER JOIN
    Clients b
        ON a.proj_clientlink = b.client_id
    )Q
WHERE Q.RN = 1
ORDER BY Q.clientname

【讨论】：

我也是！顺便说一句，它似乎没有使用Clients table。
它使用 clients 表对每个客户的结果进行排序。
我现在正在研究这些并将它们实施到我当前的项目中。我会让你知道我过得怎么样 :)
+1 是唯一一个获得“order by”权利的人。也许您应该在 row_number 部分中为列添加前缀？
是的，这段代码很有效。非常感谢所有的帮助！还有 t-clausen.dk，我不知道这意味着什么，我对 SQL 很陌生，但无论如何它都可以工作。哈哈谢谢大家！

【解决方案2】：

;with cte1 as
(
SELECT
    a.proj_name,
    a.proj_phase,
    c.proj_actions_next_action,
    c.proj_actions_next_action_date
FROM
    projects a  
LEFT OUTER JOIN
    Projects_actions c
        ON a.proj_id = c.proj_actions_projects_link
LEFT OUTER JOIN
    Clients b
        ON a.proj_clientlink = b.client_id
ORDER BY b.clientname
),
cte2 as

(
  ROW_NUMBER() OVER(PARTITION BY proj_name ORDER BY proj_actions_next_action_date DESC) AS Row,
  *
  from cte1

)

select * from cte2
where Row =1

【讨论】：