Oracle 查找与删除表中重复记录的步骤方法
作者：
案例：一个应用表中的一个字段是主键，向表中插入数据时，先把数据放在临时表中（没有主键）然后再插入应用表。
这时候如果临时表中有重复数据，无论是主键字段businessid有重复，还是一整行有重复都会报出违反唯一主键约束错误。
方法：group by XX having count(*)>1,rowid,distinct,temporary table,procedure
1、查询表中的重复数据
a.重复一个字段
b.重复多个字段
c.重复一整行
创建测试表：
复制代码 代码如下:
create table cfa (businessid number,customer varchar2(50),branchcode varchar2(10),data_date varchar2(10));
insert into cfa values (1,'Albert','SCB','2011-11-11');
insert into cfa values (2,'Andy','DB','2011-11-12');
insert into cfa values (3,'Allen','HSBC','2011-11-13');
---------------以下为重复数据----------------------------------------------
insert into cfa values (1,'Alex','ICBC','2011-11-14');
insert into cfa values (1,'Albert','CTBK','2011-11-15');
insert into cfa values (1,'Albert','SCB','2011-11-11');
对于a的情况,只有businessid重复
复制代码 代码如下:
select * from cfa where businessid in (select businessid from cfa group by businessid having count(businessid)>1);
如果是b的情况，businessid 和name同时存在重复
复制代码 代码如下:
select * from cfa where (businessid,customer) in (select businessid,customer from cfa group by businessid,customer having count(*)>1);
对于c的情况，重复一整行
参考b的方法：
复制代码 代码如下:
select * from cfa where (businessid,customer,branchcode,data_date) in (select * from cfa group by businessid,customer,branchcode,data_date having count(*)>1);
2、删除表中的重复数据
a情况，删除表中多余的重复记录，重复记录是根据单个字段（businessid）来判断，只留有rowid最小的记录
也可以只保留rowid不是最小记录，需要把代码中的min改为max这里不再赘述。
复制代码 代码如下:
delete from cfa
where businessid in (select businessid
from cfa
group by businessid
having count(businessid) > 1)
and rowid not in (select min(rowid)
from cfa
group by businessid
having count(businessid) > 1);
或者，使用下面更简单高效的语句
复制代码 代码如下:
DELETE FROM cfa t
WHERE t.ROWID >
(SELECT MIN(X.ROWID) FROM cfa X WHERE X.businessid = t.businessid);
b情况，删除表中多余的重复记录（多个字段），只留有rowid最小的记录
复制代码 代码如下:
delete from cfa
where (businessid,customer) in (select businessid,customer
from cfa
group by businessid,customer
having count(*) > 1)
and rowid not in (select min(rowid)
from cfa
group by businessid,customer
having count(*) > 1);
或者，使用下面更简单高效的语句
复制代码 代码如下:
DELETE FROM cfa t
WHERE t.ROWID > (SELECT MIN(X.ROWID)
FROM cfa X
WHERE X.businessid = t.businessid
and x.customer = t.customer);
c情况，这种情况就比较简单，使用临时表方法
复制代码 代码如下:
create table cfabak as select distinct * from cfa;
truncate table cfa;--如果是生产最好对该表backup
Insert into cfa select * from cfabak;
commit;