db2使用用户自定义函数时报错

Question

自定义函数如下：
create function a(@sno char(6))
returns table(couname char(20),score int )
language sql
reads sql data
no external action
deterministic
return
(select cname,score from grade,course where grade.sno=@sno and grade.cno=course.cno);

调用语句如下：select a('990101')
报错信息如下：
An unexpected token "END-OF-STATEMENT" was found following "select a('990101')". Expected tokens may include: "".. SQLCODE=-104, SQLSTATE=42601, DRIVER=4.7.89

函数已经成功创建了，我应该如何调用呢？