PostgreSQL中的GROUP BY和COUNT

SELECT COUNT(*) as count_all,posts.id as post_id 
FROM posts 
  INNER JOIN votes ON votes.post_id = posts.id 
GROUP BY posts.id;

在Postgresql中返回n条记录：

count_all | post_id
-----------+---------
 1         | 6
 3         | 4
 3         | 5
 3         | 1
 1         | 9
 1         | 10
(6 rows)

我只想检索返回的记录数：6。

我使用一个子查询来实现我想要的，但这似乎不是最佳的：

SELECT COUNT(*) FROM (
    SELECT COUNT(*) as count_all,posts.id as post_id 
    FROM posts 
    INNER JOIN votes ON votes.post_id = posts.id 
    GROUP BY posts.id
) as x;

在PostgreSQL中如何获取上下文中的记录数？