为什么我的存储函数用不了

delimitre @@
create function f_name(Sno varchar(20)) returns varchar(20)
begin
return(select Sname from student
where Sname=Sno);
end@@
select f_name('201215121');

单词写错了吧

delimiter @@
create function f_name(Sno varchar(20)) returns varchar(20)
begin
return(select Sname from student
where Sname=Sno);
end@@
select f_name('201215121');