sql约束有关问题，求高手解答

sql约束问题，求高手解答
学号为11位，如果不足11位或多于11位，则拒绝输入
Sno nchar（10）怎么用约束实现
create rule [dbo].[f1] as @aa like '[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]'

GO

[解决办法]

SQL code

ALTER TABLE [ta]  WITH CHECK ADD  CONSTRAINT [CK_ta_1] CHECK  (([Sno] like '[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]'))GOALTER TABLE [ta]  WITH CHECK ADD  CONSTRAINT [CK_ta] CHECK  ((len([Sno ])<=(11)))GO