select class_user.id,class_user.classid,class_user.userid from class_user inner join class_paper on class_user.classid=class_paper.classid where class_user.userid<>0 and class_user.isdel<>1 group by class_user.id,class_user.classid,class_user.userid
select distinct class_user.id,class_user.classid,class_user.userid from class_user inner join class_paper on class_user.classid=class_paper.classid where class_user.userid<>0 and class_user.isdel<>1
from class_user inner join class_paper on class_user.classid=class_paper.classid
where class_user.userid<>0 and class_user.isdel<>1
group by class_user.id,class_user.classid,class_user.userid
select distinct class_user.id,class_user.classid,class_user.userid
from class_user inner join class_paper on class_user.classid=class_paper.classid
where class_user.userid<>0 and class_user.isdel<>1