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<p><FONT class=normalfont><B><font color=blue>如何确定Oracle数据库表中重复的记录</font></B></FONT><BR><FONT class=smallfont color=#ff9900>2004-04-23 15:18 pm</FONT><BR><FONT class=normalfont>作者：石晓非<br>来自：http://www.ccidnet.com<br>联系方式：无名<br><br> 作为一个Oracle数据库开发者或者DBA，在实际工作中经常会遇到这样的问题： 试图对<br>
库表中的某一列或几列创建唯一索引时，系统提示ORA-01452：不能创建唯一索引， 发现重<br>
复记录。<br>
下面我们以表code_ref为例来讨论这个问题及其解决办法。<br>
ERROR位于第1行：<br>
ORA-01452: 无法 CREATE UNIQUE INDEX；找到重复的关键字<br>
Oracle系统提示不能对表code_ref创建一个唯一索引，因为系统发现表中存在重复的记<br>
录。我们必须首先找到表中的重复记录并删除该记录，才可以创建唯一索引。下面介绍三种<br>
不同的方法来确定库表中重复的记录。<br>
<br>
一、自关联查询方法<br>
Oracle系统中，对于所有的表都存在一个唯一的列，这就是rowid。对该列使用最大<br>
(max)或者最小(min)函数可以非常容易地确定重复的行。<br>
<br>
<br>
二、GROUP BY/HAVING查询方法<br>
利用分组函数GROUP BY/HAVING也很容易确定重复的行。 以需要创建唯一索引的列分组<br>
并统计每组的个数，很明显如果组中记录数超过1个就存在重复的行。<br>
<br>
<br>
三、Exception into子句<br>
采用alter table命令中的Exception into子句也可以确定出库表中重复的记录。 这种<br>
方法稍微麻烦一些，为了使用"excepeion into"子句，必须首先创建EXCEPTIONS表。创建该<br>
表的SQL脚本文件为utlexcpt.sql。对于NT系统和UNIX系统， Oracle存放该文件的位置稍有<br>
不同，在NT系统下，该脚本文件存放在ORACLE_HOMEOra81
dbmsadmin目录下；而对于<br>
UNIX系统，该脚本文件存放在$ORACLE_HOME/rdbms/admin目录下。<br>
<br>
ERROR位于第2行：<br>
ORA-02299：无法验证（SYSTEM.I_CODE_REF）－未找到重复关键字<br>
<br>
下面将exceptions表和code_ref表通过rowid关联起来即可得到表code_ref中重复的记录。<br>
<br>
结束<br>
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