SQL最有效的查询

我在下面的3个表上创建了两个查询，我只想听听别人对我是否最有效地执行它们的意见

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)

哪个客户部门的广告点击率最高

 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

女性最常在什么时候看广告

 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

)

---

您的第一个查询应该如下所示：

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;

注:

• 使用正确、明确的

  JOIN

  语法。切勿在

  FROM

  子句中使用逗号
• 问题是关于

  扇区

  ，在

  GROUP BY

  子句中不需要任何其他内容
• 无论如何，您不能通过聚合函数对

  进行分组

• 大概您希望通过和限制1获得顶部扇区

---

一个问题就足以回答一个问题。

对于MS SQL server，可以在所有客户端中查找点击次数最多的客户端扇区

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

---

什么是关系数据库管理系统？是mysql还是sql server？删除一个标记并将其固定到sql server-谢谢