--> 测试数据: @评论表
declare @评论表 table (ID int,视频ID int,评论内容 varchar(4),评论时间 datetime)
insert into @评论表
select 1,1,'还行','2012-03-07 12:01:02' union all
select 2,1,'不行','2012-03-08 13:11:22' union all
select 3,2,'不错','2012-03-08 12:14:26'

--> 测试数据: @点击率表
declare @点击率表 table (ID int,视频ID int,点击时间 datetime)
insert into @点击率表
select 1,1,'2012-03-07 01:02:03' union all
select 2,1,'2012-03-08 15:04:09' union all
select 3,3,'2012-03-08 18:12:14'

SELECT a.*,b.当天点击,b.一周内点击 FROM (
SELECT  ID ,
        SUM(CASE WHEN DATEDIFF(d, 评论时间, GETDATE()) = 0 THEN 1
                 ELSE 0
            END) AS 当天评论 ,
        SUM(CASE WHEN DATEDIFF(d, 评论时间, GETDATE()) < 0 THEN 1
                 ELSE 0
            END) AS 一周内评论
FROM    @评论表
GROUP BY ID
) a LEFT JOIN (
SELECT  ID ,
        SUM(CASE WHEN DATEDIFF(d, 点击时间, GETDATE()) = 0 THEN 1
                 ELSE 0
            END) AS 当天点击 ,
        SUM(CASE WHEN DATEDIFF(d, 点击时间, GETDATE()) < 0 THEN 1
                 ELSE 0
            END) AS 一周内点击
FROM    @点击率表
GROUP BY ID) b ON a.id=b.id
/*
ID          当天评论        一周内评论       当天点击        一周内点击
----------- ----------- ----------- ----------- -----------
1           0           0           0           0
2           1           0           1           0
3           1           0           1           0
*/

------解决方案--------------------

SQL code
create table 评论表(ID int,视频ID int,评论内容 varchar(20),评论时间 datetime)
insert into 评论表 values(1, 1 ,'还行', '2012-03-07 12:01:02')
insert into 评论表 values(2, 1 ,'不行', '2012-03-08 13:11:22')
insert into 评论表 values(3, 2 ,'不错', '2012-03-08 12:14:26')
create table 点击率表(ID int,视频ID int,点击时间 datetime)
insert into 点击率表 values(1, 1 ,'2012-03-07 01:02:03')
insert into 点击率表 values(2, 1 ,'2012-03-08 15:04:09')
insert into 点击率表 values(3, 3 ,'2012-03-08 18:12:14')
go

select isnull(isnull(isnull(t1.视频ID,t2.视频ID),t3.视频ID),t4.视频ID) 视频ID,
       isnull(t1.日点击量,0) 日点击量,
       isnull(t2.日评论量,0) 日评论量,
       isnull(t3.周点击量,0) 周点击量,
       isnull(t4.周评论量,0) 周评论量
from
(select 视频ID , count(1) 日点击量 from 点击率表 where datediff(dd,getdate(),点击时间) = 0 group by 视频ID) t1
full join
(select 视频ID , count(1) 日评论量 from 评论表 where datediff(dd,getdate(),评论时间) = 0 group by 视频ID) t2
on t1.视频ID = t2.视频ID
full join
(select 视频ID , count(1) 周点击量 from 点击率表 where datediff(week,getdate(),点击时间) = 0 group by 视频ID) t3
on isnull(t1.视频ID,t2.视频ID) = t3.视频ID
full join
(select 视频ID , count(1) 周评论量 from 评论表 where datediff(week,getdate(),评论时间) = 0 group by 视频ID) t4
on isnull(isnull(t1.视频ID,t2.视频ID),t3.视频ID) = t4.视频ID

drop table 评论表 ,点击率表
/*
视频ID        日点击量        日评论量        周点击量        周评论量        
----------- ----------- ----------- ----------- ----------- 
1           1           1           2           2
2           0           1           0           1
3           1           0           1           0

（所影响的行数为 3 行）
*/