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
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
from b
from b