select count(*) from (SELECT Topics.ForumID, Topics.AddedDate FROM Topics UNION ALL SELECT Replies.ForumID, Replies.AddedDate FROM Replies inner join Topics on Replies.ForumID = Topics.ForumID) as XXX where AddedDate < dateAdd(dd, -1, getdate())Topics为主题表 Replies为回复表
from
(SELECT Topics.ForumID, Topics.AddedDate
FROM Topics
UNION ALL
SELECT Replies.ForumID, Replies.AddedDate
FROM Replies inner join Topics
on Replies.ForumID = Topics.ForumID) as XXX
where AddedDate < dateAdd(dd, -1, getdate())Topics为主题表 Replies为回复表