Question

我有两张桌子：

用户
消息（其中包含 id_user AND id_user_from ）

我需要一个有关用户的基本信息列表，以及3个特殊列：

用户收到的COUNT条消息
用户发送的COUNT条消息
用户消息的所有视图（发送和接收）的总和

这是我目前的查询：

SELECT
SUM(case when message.id_user = user.id_user THEN 1 ELSE 0 END) AS q_received,
SUM(case when message.id_user_from = user.id_user THEN 1 ELSE 0 END) AS q_sent,
SUM(message.views) AS views,
user.id_user AS id_user, user.name AS name, user.lastname AS lastname, user.date_login AS date_login
FROM user
    LEFT JOIN message ON message.id_user = user.id_user
ORDER BY user.date_login DESC

总和都是错的。这是sqlfiddle，包含所有必需的表和一些记录作为示例： http://sqlfiddle.com/#!9/4fd838/2

谢谢！

Answer 1

你可以试试这个：

select t1.num as q_received, t2.num as q_sent, u.id_user from user u
left join (
 select count(*) as num, id_user from message group by id_user
) t1 on t1.id_user = u.id_user
left join (
 select count(*) as num, id_user_from from message group by id_user_from
) t2 on t2.id_user_from = u.id_user

Answer 2

我会像下面这样做：

table_a
    table_a_id number(13,0)

table_b
    table_b_id number(13,0)

table_a_b
    table_a_b_id number(13,0)
    fk_table_a_id number(13,0)
    fk_table_b_id number(13,0)

MySQL从同一个连接表中的多个列获取COUNT

2 个答案: