对两个数据库进行操作。。高手请帮忙！！！

[ganmin]

数据库assingment中有表grade,字段为stu_no,subject_name,gra.
数据库bbs中有表forum,字段为stu_no，subject_name，r_no,t_no.
现在要计算学生成绩gra，它由r_no,t_no决定，如果r_no>50,则a=50,否则a=r_no.如果t_no>50,则b=50,否则，b=r_no. gra=a+b.
大侠们，应该怎么写这条SQL语句啊？？

[asen51]

select g.stu_no,g.subject_name,gra= (case when r_no>50 then 50
else r_no end) +
(case when t_no>50 then 50
else r_no end)
from grade g inner join forum m on g.stu_no=m.stu_no

[-狙击手-]

select g.stu_no,g.subject_name,gra= (case when r_no>50 then 50
else r_no end) +
(case when t_no>50 then 50
else r_no end)
from assingment..grade g inner join bbs..forum m on g.stu_no=m.stu_no