计算用户的消息，对2个表进行1次查询

Question

有2个表：

1. 用户
2. 消息

我想要计数状态为1且状态= 2的消息。这是我试图做的事情

SELECT u.id_user, u.email, COUNT(m.id_message) as 'viewed', COUNT(m2.id_message) as 'not viewed'
FROM users u
LEFT JOIN messages m ON (u.id_user=m.id_user AND m.status=1)
LEFT JOIN messages m2 ON (u.id_user=m2.id_user AND m2.status=2)
GROUP BY u.id_user

但结果很奇怪

计数器＆＃39;查看＆＃39;并且＆＃39;不是观看＆＃39;可以是一样的。我做错了什么？

Answer 1

你可以为此

做条件和

select 
u.id_user,
u.email,
sum(case when m.status=1 then 1 else 0 end) as `viewed`,
sum(case when m.status=0 then 1 else 0 end) as `not viewed`
from users u
left join messages m on m.id_user = u.id_user
group by u.id_user,u.email