您有多条评论。因此，在加入之前：

SELECT c.num_comments,
       i.dateofcreation AS timestamp, i.userId AS userId, i.id AS ID, i.text AS Idea,
       p.permalink AS Permalink, p.name AS Username,
       SUM( vl.vote <> '' ) AS totalvotes,
       SUM( vl.vote = 1 ) AS upvote,
       SUM( vl.vote = -1 ) AS downvote
FROM idea i LEFT JOIN
     votelog vl
     ON i.id = vl.ideaid LEFT JOIN
     user u
     ON i.userId = u.id LEFT JOIN
     page p
     ON i.id = p.ideaid LEFT JOIN
     (SELECT c.ideaid, COUNT(*) as num_comments
      FROM comment c
      GROUP BY c.ideaid
     ) c
     ON c.ideaid = i.id 
GROUP BY c.num_comments,
       i.dateofcreation i.userId, i.id, i.text,
       p.permalink, p.name
ORDER BY totalvotes DESC;

笔记：
表别名使查询更易于编写和读取。
将所有未聚合的列包含在 GROUP BY （mysql的最新版本倾向于强制执行这一点）。
我猜选票是数字。把它们比作数字，而不是字符串。
mysql有一个很好的计算布尔表达式为真的次数的速记。

看来你决定加入这一行列了 comments 只数有多少评论。
但是通过这样做，您现在可以生成多个行，每个注解一行，这样就可以取消所有其他行的计数。
我建议使用标量子查询来统计注解，并删除连接。比如：

SELECT
(select count(DISTINCT comment) from comment c where c.ideaid = idea.id) AS Comment,
idea.dateofcreation AS timestamp, 
idea.userId AS userId,
idea.id AS ID,
idea.text AS Idea,
page.permalink AS Permalink,
user.name AS Username,
COUNT(CASE WHEN votelog.vote !="" THEN 1 END) AS 'totalvotes',
COUNT(CASE WHEN votelog.vote = '1' THEN 1 END) AS 'upvote',
COUNT(CASE WHEN votelog.vote = '-1' THEN 1 END) AS 'downvote'
FROM idea
LEFT JOIN votelog ON idea.id = votelog.ideaid
LEFT JOIN user ON idea.userId = user.id
LEFT JOIN page ON idea.id = page.ideaid
GROUP BY idea.id
ORDER BY totalvotes DESC