Question

我在下面的3个表格中创建了两个查询，如果我最有效地执行它们，我只想要某人的意见。

User (**user_id**, group, age, gender, timestamp, activity_type)

Client (**client_id**, sector, specified_age, specified_gender)

Advertise (a**d_id, user_id, client_id, time**, is_click, length)

哪个客户群的广告点击次数最多？

 SELECT c.client_id, c.sector, COUNT(a.is_click) as Clicked_Ads 
    FROM Advertise a, Client c
    WHERE a.client_id = c.client_id
    GROUP BY COUNT(a.is_click)
    ORDER BY c.client_id

女性什么时候最常看广告？

 SELECT a.ad_id, a.client_id, u.user_id, u.timestamps, COUNT(u.timestamps)
    FROM Advertise a, User u
    WHERE u.gender = “Female”, a.user_id = u.user_id
    ORDER BY 
    GROUP BY COUNT(u.timestamps

)

Answer 1

您的第一个查询应如下所示：

solutiondir

注意：

使用正确的，明确的SELECT c.sector, COUNT(a.is_click) as Clicked_Ads FROM Advertise a JOIN Client c ON a.client_id = c.client_id GROUP BY c.sector ORDER BY COUNT(a.is_click) DESC LIMIT 1;语法。从不在JOIN子句中使用逗号。
问题是关于FROM，sector条款中不需要任何其他内容。
无论如何，你不能GROUP BY聚合功能。
据推测，您希望GROUP BY和ORDER BY获得最高权限。

一个问题就足够了。

Answer 2

查找所有客户端点击次数最多的客户端部门，用于MS SQL服务器

SELECT TOP 1 WITH TIES client_id,sector, Clicked_Ads 
 (
   SELECT c.client_id, c.sector, SUM(a.is_click) as Clicked_Ads 
    FROM Advertise a JOIN Client c
    ON a.client_id = c.client_id
    GROUP BY c.client_id, c.sector
  )T
ORDER BY Clicked_Ads  DESC

SQL最有效的查询

2 个答案: