select studentid,attndmark
from attendance_master m,attendance_detail d
where m.attnid = d.attendid
group by studentid

并得到错误：

ORA-00979: not a GROUP BY expression

错误很好,我知道select子句中列列表的问题.但类似的查询在MysqL中是有效的.

SELECT aff.akey,username
FROM `affiliates` aff,affstats ast
WHERE aff.akey = ast.akey
group by aff.akey

我需要一个可以在RDBMS Oracle / MysqL和MSsql上运行的查询技巧.

可能是什么伎俩？