sql JOINs和COUNT

Question

说我有这个查询

 SELECT ft.*, m.*
   FROM forum_topics ft
     INNER JOIN members m ON ft.author = m.id
     WHERE ft.forum =  '$forum'
     ORDER BY ft.lastpost DESC 

我还希望从forum_replies所在的表id = ft.id获取行数。 我怎么能这样做？

Answer 1

根据您的数据库实施情况，这可能有效：

 SELECT ft.*, 
        m.*,
        ( SELECT count(1)  
            FROM forum_replies fr 
           WHERE fr.id = ft.id) AS nr_of_replies 
   FROM forum_topics ft
     INNER JOIN members m ON ft.author = m.id
     WHERE ft.forum =  '$forum'
     ORDER BY ft.lastpost DESC

HTH

Answer 2

SELECT ft.*, m.*, fr.ReplyCount
FROM forum_topics ft
INNER JOIN members m ON ft.author = m.id
inner join (
   Select Id, Count(*) as ReplyCount
   from forum_replys 
   group by id
 ) as fr 
 on ft.Id = fr.Id
 WHERE ft.forum =  '$forum'
 ORDER BY ft.lastpost DESC