SQL 数据库 - 第一个操作数

Question

这是我的数据库关系：

节目（showID、标题、premiere_year、网络、创作者、类别）

剧集（节目ID、剧集ID、播出日期、标题）

• showID 是节目的外键

演员（actID，fname，lname）

main_cast(showID, actID, role)

• showID 是显示的外键 actID 是演员的外键

recurring_cast(showID, episodeID, actID, role)

showID 是节目的外键 episodeID 是剧集的外键

• actID 是演员的外键

客户(custID, fname, lname, email, creditcard,membersince,renewaldate, password, username)

cust_queue(custID, showID, datequeued)

• custID 是客户的外键 showID 是节目的外键

观看（custID、showID、episodeID、观看日期）

• custID 是客户的外键
• showID 是节目的外键
• (showID, episodeID) 是剧集的外键
• (custID, showID) 是 cust_queue 的外键

所有的“ID”都是主键

我收到了一些疑问，对于某些人来说，我不知道该怎么做。如：

对于每个客户（显示名字和姓氏），显示哪个节目和剧集是该客户观看的第一个节目。按客户姓氏对结果进行排序。

我正在尝试：

{
SELECT FIRST (Watched.datewatched)
FROM Watched
WHERE Watched.datewatched

IN

(SELECT Customer.fname, Customer.lname, Shows.title, Episode.title 
FROM Customer, Shows, Episode, Watched
WHERE Shows.showid = Episode.showID AND Watched.custID = Customer.custID AND Watched.showID = Shows.showid
ORDER BY Watched.datewatched);
}

但我认为这是不对的。有任何想法吗？？我想我不知道如何使用“FIRST”操​​作数。

Answer 1

由于您没有提供平台，我将使用应该适用于大多数（所有）SQL 平台的代码：

以下是解决此类问题的方法，请按步骤进行。首先，我们想知道用户观看的第一期节目和剧集。

查找用户观看的第一个节目

select custID, showID, min(datewatched)
from watched
group by custID, showID

现在获取该节目的第一集

select firstshow.custID, firstshow.showID, firstshow.datewatched, minDW, mineID
from ( 
  select custID, showID, min(datewatched) as minDW
  from watched
  group by custID, showID
) as firstshow
join 
(
  select custID, showID, datewatched, min(episodeID) as mineID
  from watched
  group by custID, showID, datewatched
) as firstepisode on firstshow.custID = firstepisode.custID 
                 and firstshow.showID = firstepisode.showID
                 and firstshow.minDW = firstepisode.datewatched

现在重新加入以获取用户名和显示名称

select customer.fname, customer.lname, shows.Title as show, mineID as EpisodeNum
from ( 
  select custID, showID, min(datewatched) as minDW
  from watched
  group by custID, showID
) as firstshow
join 
(
  select custID, showID, datewatched, min(episodeID) as mineID
  from watched
  group by custID, showID, datewatched
) as firstepisode on firstshow.custID = firstepisode.custID 
                 and firstshow.showID = firstepisode.showID
                 and firstshow.minDW = firstepisode.datewatched
join customer on firstshow.custID = customer.custID
join shows on firstshow.showID = shows.showID
order by customer.lname

如果你循序渐进，即使是这样复杂的事情也可以变得简单。