在一个查询中连接几个表（包括子查询）如何更好？

Question

如何在一个查询中连接几个表（包括查询）更好？

例如，我有 2 个表：活动 (user_id, login_time) 和支付 (user_id, payment_time, amount)。两个表都有重复的 id。

任务是选择唯一的 user_id，它曾经支付过，login_time 从 05.04.12 到 10.04.12。然后按组计算总金额。

我的查询是：

SELECT t.diapason, COUNT(*) AS 'number_of_users'
FROM (SELECT CASE  
    when amount<100 then '0-100' 
    when amount>=100 then '100 +' END AS diapason
    FROM 
        (SELECT SUM(amount) AS amount 
        FROM payments GROUP BY payments.user_id) p) t
  GROUP BY t.diapason
  ORDER BY number_of_users desc;

我不知道在“2012-04-05”和“2012-04-10”之间应该在哪里使用“inner join a....”

请帮忙，谢谢！

数据样本

activity
user_id    login_time
1          05.04.2012
2          05.04.2012
3          06.04.2012
4          30.05.2012

payments
user_id    amount   payment_time
1          50       10.12.2011
1          20        09.12.2011
2          400        08.08.2011

Output for period 05.04.2012-10.04.2012

diapason     number_of_users
0-100          2
100+           1

Answer 1

我相信这会为您提供所需的内容（多种方式之一）：

SELECT t.diapason, COUNT(*) AS 'number_of_users'
FROM (SELECT CASE  
    when amount<100 then '0-100' 
    when amount>=100 then '100 +' END AS diapason
    FROM 
        (SELECT SUM(amount) AS amount 
        FROM payments 
        INNER JOIN (SELECT DISTINCT user_id FROM activity where login_time between '2012-04-05' and '2012-04-12') AS a ON payments.user_id = a.user_id
        GROUP BY payments.user_id) AS P
      ) t
GROUP BY t.diapason
  ORDER BY number_of_users desc
;