select (case when col1 isnull then 1 else 0 end)+ (case when col2 isnull then 1 else 0 end)+ (case when col3 isnull then 1 else 0 end)+ (case when col4 isnull then 1 else 0 end)+ (case when col5 isnull then 1 else 0 end)+ (case when col6 isnull then 1 else 0 end) as 空字段数 from tabname where .....
(case when col1 isnull then 1 else 0 end)+
(case when col2 isnull then 1 else 0 end)+
(case when col3 isnull then 1 else 0 end)+
(case when col4 isnull then 1 else 0 end)+
(case when col5 isnull then 1 else 0 end)+
(case when col6 isnull then 1 else 0 end) as 空字段数
from tabname
where .....