在没有重复记录的基础上可以加索引 create unique index on tablename(field); 删除重复记录可以通过rowid delete from tablename where rowid<(select max(rowid) from tablename group by field1,field2)
先删除重复记录 delete tablename where rowid not in (select max(rowid) from tablename group by field1,field2,...)field1,field2,... 所有不应该重复的列再创建主关键字 alter table tablename add constraint pk_tablename_field1 primary key (field1) /
表名:aa 字段: id varchar2(10) username varchar2(20) 现在数据库中有: ID uername 1 zheng 1 ynag 1 he 2 yahg 2 zhng 3 ge 3 li 我要id不重复,id用的是序列递增。
create table abc(id varchar2(20),username varchar2(100));
现要怎样修改之?
create unique index on tablename(field);
删除重复记录可以通过rowid
delete from tablename where rowid<(select max(rowid) from tablename group by field1,field2)
delete tablename
where rowid not in (select max(rowid) from tablename group by field1,field2,...)field1,field2,... 所有不应该重复的列再创建主关键字
alter table tablename add
constraint pk_tablename_field1 primary key (field1)
/
字段:
id varchar2(10) username varchar2(20)
现在数据库中有:
ID uername
1 zheng
1 ynag
1 he
2 yahg
2 zhng
3 ge
3 li
我要id不重复,id用的是序列递增。