📄 oracle sql性能优化系列 (十)-1-acnow_net.htm
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<H1>ORACLE SQL性能优化系列 (十)</H1>
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<TD align=middle height=20>http://Tech.acnow.net 2005-4-29 <FONT color=#a20010>网络</FONT></TD>
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<TD class=l17><FONT class=f14 id=zoom><BR><BR> 1 0 TABLE ACCESS (BY INDEX ROWID) OF 'EMP'<BR><BR> 2 1 INDEX (RANGE SCAN) OF 'EMPNO' (UNIQUE) <BR><BR> <BR><BR>SQL> select * from emp where empno <= 1;<BR><BR>no rows selected<BR><BR>Execution Plan<BR><BR>----------------------------------------------------------<BR><BR> 0 SELECT STATEMENT Optimizer=CHOOSE<BR><BR> 1 0 TABLE ACCESS (BY INDEX ROWID) OF 'EMP'<BR><BR> 2 1 INDEX (RANGE SCAN) OF 'EMPNO' (UNIQUE)<BR><BR> <BR><BR> 两者的效率完全一样，也许这符合作者关于” 在某些时候, ORACLE优化器会自动将NOT转化成相对应的关系操作符” 的观点．<BR><BR> <BR><BR>35. 用>=替代><BR><BR> <BR><BR>如果DEPTNO上有一个索引, <BR><BR> <BR><BR>高效:<BR><BR> <BR><BR> SELECT *<BR><BR> FROM EMP<BR><BR> WHERE DEPTNO >=4<BR><BR> <BR><BR> 低效:<BR><BR> <BR><BR> SELECT *<BR><BR> FROM EMP<BR><BR> WHERE DEPTNO >3<BR><BR> <BR><BR> 两者的区别在于, 前者DBMS将直接跳到第一个DEPT等于4的记录而后者将首先定位到DEPTNO=3的记录并且向前扫描到第一个DEPT大于3的记录.<BR><p><div align="right">本新闻共<font color=red>2</font>页,当前在第<font color=red>2</font>页 <a href="164559059816455944859.shtml">1</a> <font color="red">2</font> </div></p>
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<td><img src="http://tech.acnow.net/Files/Img/list_nav_spacer.gif"><a Class="a2" href= http://tech.acnow.net/Html/DataBase/Oracle/2005-4/29/164558059816455810544.shtml title="ORACLE SQL性能优化系列 (一)">ORACLE SQL性能优化系列 (一)</a></td></tr>
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<td><img src="http://tech.acnow.net/Files/Img/list_nav_spacer.gif"><a Class="a2" href= http://tech.acnow.net/Html/DataBase/Oracle/2005-4/29/164559059816455980543.shtml title="ORACLE SQL性能优化系列 (十二)">ORACLE SQL性能优化系列 (十二)</a></td></tr>
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<td><img src="http://tech.acnow.net/Files/Img/list_nav_spacer.gif"><a Class="a2" href= http://tech.acnow.net/Html/DataBase/Oracle/2005-4/29/16455905981645592205.shtml title="ORACLE SQL性能优化系列 (十三)">ORACLE SQL性能优化系列 (十三)</a></td></tr>
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<td><img src="http://tech.acnow.net/Files/Img/list_nav_spacer.gif"><a Class="a2" href= http://tech.acnow.net/Html/DataBase/Oracle/2005-4/29/164558059816455862139.shtml title="ORACLE SQL性能优化系列 (二)">ORACLE SQL性能优化系列 (二)</a></td></tr>
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<td><img src="http://tech.acnow.net/Files/Img/list_nav_spacer.gif"><a Class="a2" href= http://tech.acnow.net/Html/DataBase/Oracle/2005-4/29/164558059816455832996.shtml title="ORACLE SQL性能优化系列 (四)">ORACLE SQL性能优化系列 (四)</a></td></tr>
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<td><img src="http://tech.acnow.net/Files/Img/list_nav_spacer.gif"><a Class="a2" href= http://tech.acnow.net/Html/DataBase/Oracle/2005-4/29/164559059816455960820.shtml title="ORACLE SQL性能优化系列 (十四) 完结篇">ORACLE SQL性能优化系列 (十四) 完结篇</a></td></tr>
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<td><img src="http://tech.acnow.net/Files/Img/list_nav_spacer.gif"><a Class="a2" href= http://tech.acnow.net/html/SoftWare/SoftwareEducate/OracleAuthentication/2006-5/29/150826355.shtml title="ORACLE SQL性能优化系列 (一)">ORACLE SQL性能优化系列 (一)</a></td></tr>
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