Question

我正在努力解决这个SQL查询问题。说我有这两个表

**USERS**
+----+-------+
| id | name  |
+----+-------+
|  1 | james |
|  2 | tom   |
|  3 | kate  |
+----+-------+

**PHOTOS**
+-----------+-----------+---------+
|   name    | sent_from | sent_to |
+-----------+-----------+---------+
| beach.jpg |         1 |       2 |
| trees.jpg |         3 |       1 |
| earth.jpg |         2 |       1 |
+-----------+-----------+---------+

如何使用一个SQL查询获得与其id相关联的sent_to多于sent_from的所有用户？

Answer 1

我认为这可能会对你有所帮助：

    SELECT * FROM (
       SELECT `id`, `name`, 
       IFNULL((SELECT count(*) FROM `photos` WHERE `sent_from` = `users`.`id`),0) AS `sent_from_count`,
       IFNULL((SELECT count(*) FROM `photos` WHERE `sent_t`o = `users`.`id`),0) AS `sent_to_count`
       FROM `users`) AS `t1`
    WHERE `t1`.`sent_to_count` > `t1`.`sent_to_count`

Answer 2

我认为这是将数据聚合两次然后进行比较：

select sf.sent_from
from (select sent_from, count(*) as numsent
      from photos
      group by sent_from
     ) sf left outer join
     (select sent_to, count(*) as numrecv
      from photos
      group by sent_to
     ) st
     on sf.sent_from, st.sent_to
where numsent > numrecv;

如果您需要用户信息，请将其加入。

另一种方法是首先重构数据，然后进行聚合：

select who
from (select sent_from as who, 1 as sent_from, 0 as sent_to
      from photos
      union all
      select sent_to as who, 0, 1
      from photos
     ) p
group by who
having sum(sent_from) > sum(sent_to);

选择收到的照片数量多于发送照片数量的用户

2 个答案: