sql命令由另一個值限制

Question

所以，我有2個表，release和release_favourites。

發布結構：

  id    date (timestamp)    other data
  1     1486901083          ...
  2     1486909903          ...
  ....

release_favourites結構：

  id    releaseId    userId
  1     2            5
  2     2            10
  ....

我想按日期排序記錄（這在SQL中是沒有問題的），但是我只希望最喜歡的10條記錄可以嗎？

（下面的SQL有效，但僅適用於按日期排序）

SELECT [some rows]
FROM release AS a, release_favourites AS b
WHERE a.id = b.releaseId
ORDER BY a.date

Answer 1

select      *

from        release

where       id in
            (
                select      releaseid
                from        release_favourites
                group by    releaseid
                order by    count(*) desc
                limit       10
            )

order by    date

Answer 2

根據您的描述，您需要GROUP BY 。 您僅顯示一個表（盡管查詢有兩個表）。 這是您想要的（合理的）猜測：

select rf.release_id
from release_favourites rf
group by rf.release_id
order by count(*) desc
fetch first 10 rows only;

您可以在任何領域，你實際上是從另一個表要加入（或使用in或exists ）。 並非所有數據庫都支持ANSI標准fetch first 10 rows only語法。 但是，所有方法都可以將結果集限制為給定的行數。

Answer 3

SELECT DISTINCT [some rows]
FROM release 
WHERE id IN (
       SELECT releaseId 
       FROM (
              SELECT releaseId
              FROM release_favourite
              GROUP BY releaseId
              ORDER BY count(*) 
              DESC LIMIT 10
       )
       AS tmp
)
ORDER BY date