Question

我的第一个问题：

`SELECT M.type, U.campaign_id, count(*) as NumEvents 
 FROM dbo.Events E 
 JOIN dbo.Meals M
 ON E.meal_id = M.meal_id 
 JOIN dbo.Users U
 ON U.userid = E.userid
 GROUP BY M.type, U.campaign_id
 ORDER BY M.type`

这给了我这个结果：

TYPE         Campaign-id       # of Events
Chinese        FB                2
Chinese        RE                1
Chinese        TW                2
French         FB                1
French         PI                2
French         RE                2
Italian        FB                3
Italian        RE                2
Italian        TW                2
Mexican        RE                1

如果类型是膳食的类型，则Campaign_id指的是吃饭的人的类型，并且＃个事件是指具有特定Campaign_id的人吃了某种类型的膳食的次数。

我需要一个SQL Server查询，它会为我提供与每种膳食类型的大多数事件相关联的Campaign_id。谢谢

结果应如下所示：

TYPE         Campaign-id with Greatest Number of events
Chinese               FB or TW                
French                RE or PI              
Italian               FB                
Mexican               RE

Answer 1

首先，简化您现有的查询：

SELECT m.type, U.campaign_id, count(*) as NumEvents
FROM dbo.Events E JOIN
     dbo.Meals M
     ON E.meal_id = M.meal_id JOIN
     dbo.Users U
     ON U.userid = E.userid
GROUP BY m.type, U.campaign_id;

然后，让我们解决这个问题，以获得你想要的东西：

SELECT mc.*
FROM (SELECT m.type, U.campaign_id, count(*) as NumEvents,
             ROW_NUMBER() OVER (PARTITION BY m.type ORDER BY COUNT(*) DESC) as seqnum
      FROM dbo.Events E JOIN
           dbo.Meals M
           ON E.meal_id = M.meal_id JOIN
           dbo.Users U
           ON U.userid = E.userid
      GROUP BY m.type, U.campaign_id
     ) mc
WHERE seqnum = 1;

SQL - 仅显示不同类别的类型名称的最大类型＃

1 个答案: