SELECT
    CONVERT(VARCHAR(10), [注册时间], 120) AS [注册时间],
    COUNT(DISTINCT [注册人数]) AS [注册人数],
    COUNT(DISTINCT [注册类型]) AS [注册类型]
FROM
    (
     SELECT
        [registTime] AS 注册时间,
        [telNo] AS 注册人数,
        [registType] AS 注册类型
     FROM
        [T_onLine]
     WHERE
        (
         [registTime] IS NOT NULL
         AND [registTime] <> '' --如果是registTime是DateTime类型的,这句多余,并且会影响性能
        )
        AND [registTime] BETWEEN '2011-11-22 23:59:59.999' --考虑registTime字段的类型
                         AND     '2011-11-24 00:00:00.000'
        AND [registType] NOT IN ('9994', '9995', '9998')
     UNION --如果2个union的结果集肯定不会有重复的值,就用union all
     SELECT
        [registTime] AS 注册时间,
        [telNo] AS 注册人数,
        [registType] AS 注册类型
     FROM
        [T_unRegistLog]
     WHERE
        (
         [registTime] IS NOT NULL
         AND [registTime] <> ''
        )
        AND [registTime] BETWEEN '2011-11-22 23:59:59.999' --registTime建立索引
                         AND     '2011-11-24 00:00:00.000'
        AND [registType] NOT IN ('9994', '9995', '9998')
        AND [telNo] NOT IN (SELECT  --telNo建立索引
                                [telNo]
                            FROM
                                [T_onLine])
    ) T
GROUP BY
    CONVERT(VARCHAR(10), [注册时间], 120)

------解决方案--------------------
嵌套即可。
select convert(varchar(10),[注册时间],120) as [注册时间]
 ,count(distinct [注册人数]) as [注册人数]
 ,count(distinct [注册类型]) as [注册类型]
from (select [registTime] as 注册时间
 	,[telNo] as 注册人数
 	,[registType] as 注册类型  
	from [T_onLine]
	where([registTime] is not null and [registTime]<>'')
 	and[registTime] between '2011-11-22 23:59:59.999'and '2011-11-24 00:00:00.000'
 	and[registType] not in('9994','9995','9998')
	union 
	select [registTime] as 注册时间
 	,[telNo] as 注册人数
 	,[registType] as 注册类型
	from [T_unRegistLog]
	where([registTime] is not null and [registTime]<>'')
 	and[registTime] between '2011-11-22 23:59:59.999'and '2011-11-24 00:00:00.000'
 	and[registType] not in('9994','9995','9998')
 	and [telNo] not in (select [telNo] from [T_onLine])) [临时表3]
group by convert(varchar(10),[注册时间] ,120)

------解决方案--------------------
SQL code
select convert(varchar(10),[注册时间],120) as [注册时间]
  ,count(distinct [注册人数]) as [注册人数]
  ,count(distinct [注册类型]) as [注册类型]
from (select [registTime] as 注册时间
  ,[telNo] as 注册人数
  ,[registType] as 注册类型   
from [T_onLine]
where([registTime] is not null and [registTime]<>'')
  and[registTime] between '2011-11-22 23:59:59.999'and '2011-11-24 00:00:00.000'
  and[registType] not in('