在oracle的複雜查詢中獲取最後的論壇海報

Question

我在爲應用程序構建一個論壇，並且我試圖在討論中獲取最新的海報。我正在使用的數據庫是Oracle。

我有以下表格：

discussions 
    id 
    course_id 
    user_id 
    title 
    stub 
    created_at 

threads 
    id 
    discussion_id 
    user_id 
    created_at 
    updated_at 
    message 

discussion_views 
    discussion_id 
    user_id 
    time 

users 
    id 
    username 

而且我有以下查詢：

select discussions.created_at, 
     discussions.title, 
     users.username, 
     count(threads.id) AS "replies", 
     count(distinct discussion_views.discussion_id) AS "views" 
from discussions 
left join threads on discussions.id=threads.discussion_id 
left join discussion_views on discussions.id=discussion_views.discussion_id 
join users on users.id=discussions.user_id 
group by discussions.created_at, discussions.title, users.username 
order by discussions.created_at desc 

我需要的是讓誰張貼在一個線程和日期的最後一個用戶。我應該製作一個內插件，一個連接還是應該製作另一個插件。我也希望我的查詢是高性能的，因爲我的論壇需要處理大量的流量。

Answer 1

嘗試：

select * from 
(select discussions.created_at, 
     discussions.title, 
     users.username as discussion_created_by, 
     count(distinct threads.id) over (partition by discussions.created_at, 
                 discussions.title, 
                 users.username) AS replies, 
     count(distinct discussion_views.time) 
      over (partition by discussions.created_at, 
           discussions.title, 
           users.username) AS "views", 
     threads.user_id AS latest_post_by, 
     threads.updated_at AS latest_post_at, 
     row_number() over (partition by discussions.created_at, 
             discussions.title, 
             users.username 
          order by threads.id desc) AS rn 
from discussions 
left join threads on discussions.id=threads.discussion_id 
left join discussion_views on discussions.id=discussion_views.discussion_id 
join users on users.id=discussions.user_id) sq 
where rn=1 
order by created_at desc