来自相对表的SELECT和COUNT

Question

我有两个表，论坛和主题。每个主题都属于一个论坛，由forum_id指定。对于每个论坛，我想在同一查询中返回所属的主题。

SELECT  (
SELECT *
FROM  forums
) AS forums,
(
SELECT COUNT(*)
FROM  topics t
WHERE t.forum_id=forums.id
) AS topic_count

如何从第一个选择中传递ID并在第二个中进行比较？

Answer 1

这是你想要的吗？

SELECT f.*, COUNT(*)
FROM forums f
     topics t
     on t.forum_id = forums.id
GROUP BY f.id;

Answer 2

Select *, (Select Count(*) From topics t2 
    Where t2.forum_id=t1.Forums_id) As [Topic Count] 
    From forums t1
    Order By t1.forums_id