C列也要考虑对么？
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delete from table x
where not exists (select 1 from (select a,b,max(c) c from table group by a,b ) y
where x.a=y.a and x.b=y.b and x.c=y.c);
随机删除重复列：
delete from table x
where exists(select 1 from (select a, b, max(rowid) max_rowid from table group by a, b) y
where x.a=y.a and x.b=y.b and x.rowid y.max_rowid);
先去重再导入。
删除表中多余的重复记录（多个字段），只留有rowid最小的记录
delete from 表 a
where (a.Id,a.seq) in
(select Id,seq from 表 group by Id,seq having count(*) 1)
and rowid not in
(select min(rowid) from 表 group by Id,seq having count(*)1)
1。用rowid方法
据据oracle带的rowid属性，进行判断，是否存在重复,语句如下：
查数据:
select * from table1 a where rowid
!=(select max(rowid)
from table1 b where a.name1=b.name1 and
a.name2=b.name2......)
删数据：
delete from table1 a where rowid
!=(select max(rowid)
from table1 b where a.name1=b.name1 and
a.name2=b.name2......)
2.group by方法
查数据:
select count(num), max(name) from student --列出重复的记录数，并列出他的name属性
group by num
having count(num) 1 --按num分组后找出表中num列重复，即出现次数大于一次
删数据：
delete from student
group by num
having count(num) 1
这样的话就把所有重复的都删除了。
3.用distinct方法 -对于小的表比较有用
create table table_new as select distinct *
from table1 minux
truncate table table1;
insert into table1 select * from table_new;
