sql语句请教(两张表)

[ibm_qq]

Topic(主题表) Reply(回复表)
TopicID Title ReplyID TopicID
1 AA 1 3
2 BB 2 3
3 CC 3 2
4 DD

想通过sql语句得到
TopicID Title ReplyNum
1 AA 0
2 BB 1
3 CC 2
4 DD 0

请教

[lsqkeke]

select TopicID,
Title,
ReplyNum=select count(1) from Reply where TopicID=a.TopicID
from TopicID a

[lsqkeke]

select TopicID,
Title,
ReplyNum=isnull((select count(1) from Reply where TopicID=a.TopicID),0)
from TopicID a