--数据库多字段去重
delete from student a where (a.no,a.name,a.science)in (select a.no,a.name,a.science from student a
group by a.no,a.name,a.science having count(*) > 1)
and rowid not in (select min(rowid) from student a group by a.no,a.name,a.science having count(*)>1);