》》情景:库表中有多条重复数据,请用SQL实现删除一条保留一条。
--创建表SQL create table TEMP ( ID number,--主键 name varchar2(50), insert_date date );
》》实现方式:
--查询出所有有重复的数据SQL select ID,name,count(ID) from TEMP group by name,ID having count(ID)>1 order by ID ;
若 主键不重复
--删除重复的数据,保留最小ID值的SQL delete from TEMP where ID not in ( select min(ID) from TEMP group by name ); --扩展 delete from TEMP where name in ( select name from TEMP GROUP BY name having count(name) > 1) and ID not in ( select min(ID) from TEMP groupby name );
若主键也重复
--删除重复的数据,保留最小ID值的SQL delete from TEMP where name in( selecct name from temp group by name having count(name) > 1 ) and rowid not in ( select min(rowid) from TEMP group by name having count(name) > 1 );
补充:ROWID:数据库中行的全局唯一地址,通常来说,一个rowid值唯一标识数据中的一行.