奇怪啊，我用Pivot怎么出问题呢？

[superhasty]

表数据如下：

ID U_Name SP_ID Month_Fee
1 zhang 笑话 3.00
2 ma 天气 5.00
3 zhang 健康 4.00
4 zhang 交通 6.00
5 ma 彩票 10.00

用下面的SQL语句
SELECT U_name,[笑话] as 笑话,[健康] as 健康,[天气] as 天气 FROM tab_Fee
PIVOT(
SUM(Month_Fee)
FOR SP_Code IN
([笑话],[健康],[天气])
) AS pvt

怎么查询的结果是这样的？
U_name 笑话 健康 天气
ma NULL NULL 5.00
ma NULL NULL NULL
zhang 3.00 NULL NULL
zhang NULL 4.00 NULL
zhang NULL NULL NULL

[superhasty]

我以为应该得到这样的结果：
U_name 笑话 健康 天气
ma .00 .00 5.00
zhang 3.00 4.00 .00

可为什么没有得到呢？

[子陌红尘]

SELECT
U_name,
isnull(max([笑话]),0.00) as 笑话,
isnull(max([健康]),0.00) as 健康,
isnull(max([天气]),0.00) as 天气
FROM tab_Fee
PIVOT(
SUM(Month_Fee)
FOR SP_Code IN
([笑话],[健康],[天气])
) AS pvt

[superhasty]

to
我的机器上这样写才是正确的：
SELECT
U_name,
isnull(max([笑话]),0.00) as 笑话,
isnull(max([健康]),0.00) as 健康,
isnull(max([天气]),0.00) as 天气
FROM tab_Fee
PIVOT(
SUM(Month_Fee)
FOR SP_Code IN
([笑话],[健康],[天气])
) AS pvt
group by U_name