方法一：
delete from dbyh where yhbh in(select yhbh from dbyh group by yhbh having count(*)>1) and
rowid not in (select min(rowid) from dbyh group by yhbh having count(*)>1);
方法二：
create table dbyh_tmp as select distinct * from dbyh;
drop table dbyh;
alter table dbyh_tmp rename to dbyh;
