MySQL 使用 RIGHT JOIN 获取项目计数

Question

我需要收集一位用户创建的所有帖子并获取加入这些帖子的人数。

我尝试过这个查询:

SELECT ads.id, ads.title, sign_ups.user_id
FROM sign_ups RIGHT JOIN ads ON ads.id = sign_ups.ad_id
WHERE advertiser_id=1

输出是:

id      title                  user_id
1      Something                  1
2      something else             2
3      another title             NULL
1      Something                  2

但我想要:

id      title               total
1      Something              2
2      something else         1
3      another title          0

但我想要:

id      title               total
1      Something              2
2      something else         1
3      another title          0

所以我尝试过这个:

SELECT ads.id, ads.title, count(sign_ups.user_id) AS total
FROM sign_ups
RIGHT JOIN ads ON ads.id = sign_ups.ad_id
WHERE advertiser_id =1

但输出不包括所有没有关注用户的 title 字段。所以结果看起来像这样:

id      title                  total
1      Something                 2
2      something else            1

想问一下，如何更改我的查询以获取所有想要的记录。

谢谢!

Answer 1

试试这个:

SELECT ads.id, ads.title, count(sign_ups.user_id) AS total
FROM sign_ups
RIGHT JOIN ads ON ads.id = sign_ups.ad_id
WHERE advertiser_id=1 AND sign_ups.user_id IS NOT NULL
UNION ALL
SELECT ads.id, ads.title, 0 AS total
FROM sign_ups
RIGHT JOIN ads ON ads.id = sign_ups.ad_id
WHERE advertiser_id=1 AND sign_ups.user_id IS NULL