查询时null不要显示
表如下：
user_name user_pd
------------------------------
wang 1
wang <NULL>

我要用SELECT user_name,CONVERT(char(10), user_pd) user_pd from b 来查询
效果是：
user_name user_pd
------------------------------
wang 1
wang

[解决办法]
is null
[解决办法]
SELECT user_name,isnull(user_pd, ' ') as user_pd
from b
[解决办法]
--如果user_pd是数字型

SELECT user_name,isnull(rtrim(user_pd), ' ') as user_pd
from b