��翼渐丰 — Tue, 08 Jan 2008 02:04:00 GMT

今天google分析函数row_number()的时候发现的�Q�觉得很好：

表demo是重复拷贝自dba_objects�Q�有88万左叻I��不重复的�?7323�Q�没有烦�?br style="font-family: " /> �Ҏ��一�Q�delete from demo a where a.rowid <> (select max(rowid) from demo b where
b.object_id=a.object_id);
耗时�Q�几个小时以�?
�Ҏ��二： delete from demo where rowid in
(select rid from
(select rowid rid,row_number() over(partition by object_id order by rowid) rn
from demo)
where rn <> 1 );
耗时�Q?0�U?br style="font-family: " /> �Ҏ��三： create table demo2 as
select object_id,owner... from
(select demo.*,row_number() over(partition by object_id order by rowid) rn from demo)
where rn = 1;
truncate table demo; insert into demo select * from demo2; drop table demo2;
��p��时�Q?10�U�，适合大数据量的情况，产生更少回滚量；

学到了分析函数row_number(),对于object_id和rowid也有了一些认识。oracle要学的东西太多了�Q�什么时候是个头�?img alt="" src="/CuteSoft_Client/CuteEditor/images/emteeth.gif" align="absMiddle" border="0" />。上面的�Ҏ��不是很难理解�Q�但也还没有完全理解�Q�有��Z��实际试试�?/p>

��翼渐丰 2008-01-08 10:04 发表评论

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