数据库删除完全重复和部分关键字段重复的记录
<p>1、第一种重复很容易解决，不同数据库环境下方法相似： <br><br>
以下为引用的内容：<br>
Mysql <br><br>
create table tmp select distinct * from tableName; <br><br>
drop table tableName; <br><br>
create table tableName select * from tmp; <br><br>
drop table tmp; <br><br><br>
SQL Server <br><br>
select distinct * into #Tmp from tableName; <br><br>
drop table tableName; <br><br>
select * into tableName from #Tmp; <br><br>
drop table #Tmp; <br><br>
Oracle <br><br>
create table tmp as select distinct * from tableName; <br><br>
drop table tableName; <br><br>
create table tableName as select * from tmp; <br><br>
drop table tmp; <br><br><br><br>
发生这种重复的原因是由于表设计不周而产生的，增加唯一索引列就可以解决此问题。 <br><br>
2、此类重复问题通常要求保留重复记录中的第一条记录，操作方法如下。 假设有重复的字段为Name,Address，要求得到这两个字段唯一的结果集 <br><br>
Mysql <br><br>
以下为引用的内容：<br>
alter table tableName add autoID int auto_increment not null; <br><br>
create table tmp select min(autoID) as autoID from tableName group by Name,Address; <br><br>
create table tmp2 select tableName.* from tableName,tmp where tableName.autoID = tmp.autoID; <br><br>
drop table tableName; <br><br>
rename table tmp2 to tableName; <br><br>
SQL Server <br><br>
select identity(int,1,1) as autoID, * into #Tmp from tableName; <br><br>
select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,Address; <br><br>
drop table tableName; <br><br>
select * into tableName from #Tmp where autoID in(select autoID from #Tmp2); <br><br>
drop table #Tmp; <br><br>
drop table #Tmp2; <br><br>
Oracle <br><br>
DELETE FROM tableName t1 WHERE t1.ROWID > (SELECT MIN(t2.ROWID) FROM tableName t2 WHERE t2.Name = t1.Name and t2.Address = t1.Address); <br><br>
<br><br><br>
说明： <br><br>
1. MySQL和SQL Server中最后一个select得到了Name，Address不重复的结果集（多了一个autoID字段，在大家实际写时可以写在select子句中省去此列） <br><br>
2. 因为MySQL和SQL Server没有提供rowid机制，所以需要通过一个autoID列来实现行的唯一性，而利用Oracle的rowid处理就方便多了。而且使用ROWID是最高效的删除重复记录方法。</p>
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