oracle 查询重复数据并且删除, 只保留一条数据

数据库操作中，经常会因为导数据造成数据重复，需要进行数据清理，去掉冗余的数据，只保留正确的数据

一：重复数据根据单个字段进行判断

1、首先，查询表中多余的数据，由关键字段（name）来查询。

select * from OA_ADDRESS_BOOK where name in (select name from OA_ADDRESS_BOOK group by name having count(name)>1)

2、删除表中重复数据，重复数据是根据单个字段（Name）来判断，只留有rowid最小的记录

delete from OA_ADDRESS_BOOK where (Name) in

(select Name from OA_ADDRESS_BOOK group by Name having count(Name) >1)

and rowid not in (select min(rowid) from OA_ADDRESS_BOOK group by Name having count(Name)>1)

二：重复数据根据多个字段进行判断

1、首先，查询表中重复数据，由关键字段（Name,UNIT_ID）来查询。

select * from OA_ADDRESS_BOOK book1 where (book1.name,book1.unit_id) in 
(select book2.name,book2.unit_id from OA_ADDRESS_BOOK book2 group by  book2.name,book2.unit_id  having count(*)>1)

2、删除表中重复数据，重复数据是根据多个字段（Name,UNIT_ID）来判断，只留有rowid最小的记录

delete from OA_ADDRESS_BOOK a where (a.Name,a.UNIT_ID) in 
(select Name,UNIT_ID from OA_ADDRESS_BOOK group by Name,UNIT_ID having count(*) > 1) 
and rowid not in (select min(rowid) from OA_ADDRESS_BOOK group by Name,UNIT_ID having count(*)>1)

3、查询表中重复数据，重复数据是根据多个字段（Name,UNIT_ID）来判断，不包含rowid最小的记录

select name,unit_id from OA_ADDRESS_BOOK a where (a.Name,a.UNIT_ID)
in 
(select Name,UNIT_ID from OA_ADDRESS_BOOK group by Name,UNIT_ID having count(*) > 1) 
and rowid not in (select min(rowid) from OA_ADDRESS_BOOK group by Name,UNIT_ID having count(*)>1)