如何创建合适的索引－主要是创建多列索引还是单列索引？

末蓝、 2022-05-29 08:17 225阅读 0赞

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       <span style="word-wrap:break-word">发表于 2004-12-8 15:21</span>&nbsp; 
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          <td style="word-wrap:break-word; font-size:14px"> <span style="word-wrap:break-word; font-weight:700"><span style="color:#FF0000; word-wrap:break-word"></span></span>如我有一个表<br style="word-wrap:break-word"> UserInfo<br style="word-wrap:break-word"> { <br style="word-wrap:break-word"> &nbsp; &nbsp;id number(10,0) not null,<br style="word-wrap:break-word"> &nbsp; &nbsp;username varchar(100) not null,<br style="word-wrap:break-word"> &nbsp; &nbsp;realname varchar(100) not null,<br style="word-wrap:break-word"> &nbsp; &nbsp;<a href="http://www.itpub.net/tree/index_339/" style="word-wrap:break-word; color:rgb(51,102,153); border-bottom:1px solid blue" rel="nofollow">bi</a>rthday date not null<br style="word-wrap:break-word"> }<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 其中id列是PK，username 是唯一键(unique)<br style="word-wrap:break-word"> 以上四列经常被当作条件放到where 字句里面。<br style="word-wrap:break-word"> 我是分别在每一列上创建一个索引，还创建一个索引包含一列呢？<br style="word-wrap:break-word"> 请多指教！！<br style="word-wrap:break-word"> 如：<br style="word-wrap:break-word"> 1）select * from userInfo where id = 10;<br style="word-wrap:break-word"> select * from userInfo where username = '1111';<br style="word-wrap:break-word"> select * from userInfo where name = '1111';<br style="word-wrap:break-word"> select * from userInfo where birthday= to_date('2003-10-10','yyyy-mm-dd');<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 这个肯定创建单列索引了<br style="word-wrap:break-word"> 2）select * from userinfo where&nbsp;&nbsp;name = '2222' and birthday= to_date('2003-10-10','yyyy-mm-dd');<br style="word-wrap:break-word"> 如何创建索引？？<br style="word-wrap:break-word"> 3）select * from userinfo where&nbsp;&nbsp;id = 1111 and name = '2222' and birthday= to_date('2003-10-10','yyyy-mm-dd');</td> 
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       <img src="http://www.itpub.net/static/image/common/online_moderator.gif" alt="" style="word-wrap:break-word; vertical-align:middle; width:16px">&nbsp; 
       <span style="word-wrap:break-word">发表于 2004-12-26 17:27</span>&nbsp; 
       <span style="word-wrap:break-word; margin:0px 5px; color:rgb(204,204,204)">|</span>&nbsp; 
       <a href="http://www.itpub.net/forum.php?mod=viewthread&amp;tid=298746&amp;page=1&amp;authorid=48934" style="word-wrap:break-word; color:rgb(51,51,51)" rel="nofollow">只看该作者</a> 
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            <blockquote style="word-wrap:break-word; display:inline-block; margin:0px; padding:0px 65px 5px 0px; line-height:1.6; zoom:1"> 
             <span style="word-wrap:break-word">最初由 oracle-plus 发布</span> 
             <br style="word-wrap:break-word"> [B] 
             <br style="word-wrap:break-word"> 有一點也注意的是：如果索引是建立在多个列上, 只有在它的第一个列(leading column)被where子句引用时,优化器才会选择使用该索引。 
             <br style="word-wrap:break-word"> 所以，你要根據你的查詢需求來決定是否使用Composite Indexes [/B] 
            </blockquote> 
           </div> <br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 这个是8i的限制，9i不是这样了</td> 
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     <span style="word-wrap:break-word"><a href="http://www.itpub.net/forum.php?mod=redirect&amp;goto=findpost&amp;ptid=298746&amp;pid=2061551" style="word-wrap:break-word; color:rgb(51,51,51); float:right; margin-top:-6px; padding:4px 6px; font-weight:400" rel="nofollow"><span style="word-wrap:break-word">6</span><sup style="word-wrap:break-word">#</sup></a></span> 
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       <img src="http://www.itpub.net/static/image/common/online_moderator.gif" alt="" style="word-wrap:break-word; vertical-align:middle; width:16px">&nbsp; 
       <span style="word-wrap:break-word">发表于 2004-12-26 18:05</span>&nbsp; 
       <span style="word-wrap:break-word; margin:0px 5px; color:rgb(204,204,204)">|</span>&nbsp; 
       <a href="http://www.itpub.net/forum.php?mod=viewthread&amp;tid=298746&amp;page=1&amp;authorid=16648" style="word-wrap:break-word; color:rgb(51,51,51)" rel="nofollow">只看该作者</a> 
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          <td style="word-wrap:break-word; font-size:14px"> 三个索引足了<br style="word-wrap:break-word"> 1 id上的主键<br style="word-wrap:break-word"> 2 username上的unique index<br style="word-wrap:break-word"> 3 name+birthday的组合索引</td> 
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   <td style="word-wrap:break-word; vertical-align:top; width:160px; overflow:hidden; border-right:1px solid rgb(255,255,255)"> &nbsp;</td> 
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     <span style="word-wrap:break-word"><a href="http://www.itpub.net/forum.php?mod=redirect&amp;goto=findpost&amp;ptid=298746&amp;pid=8984592" style="word-wrap:break-word; color:rgb(51,51,51); float:right; margin-top:-6px; padding:4px 6px; font-weight:400" rel="nofollow"><span style="word-wrap:break-word">7</span><sup style="word-wrap:break-word">#</sup></a></span> 
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       <img src="http://www.itpub.net/static/image/common/online_member.gif" alt="" style="word-wrap:break-word; vertical-align:middle; width:16px">&nbsp; 
       <span style="word-wrap:break-word">发表于 2007-11-15 18:15</span>&nbsp; 
       <span style="word-wrap:break-word; margin:0px 5px; color:rgb(204,204,204)">|</span>&nbsp; 
       <a href="http://www.itpub.net/forum.php?mod=viewthread&amp;tid=298746&amp;page=1&amp;authorid=7659204" style="word-wrap:break-word; color:rgb(51,51,51)" rel="nofollow">只看该作者</a> 
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           <div style="word-wrap:break-word; overflow:hidden; margin:10px 0px; padding:10px 10px 5px 65px; color:rgb(102,102,102); zoom:1"> 
            <blockquote style="word-wrap:break-word; display:inline-block; margin:0px; padding:0px 65px 5px 0px; line-height:1.6; zoom:1"> 
             <span style="word-wrap:break-word">最初由 grassbell 发布</span> 
             <br style="word-wrap:break-word"> [B] 
             <br style="word-wrap:break-word"> 
             <br style="word-wrap:break-word"> 这个是8i的限制，9i不是这样了 [/B] 
            </blockquote> 
           </div> <br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 这个要看sql怎么写的。<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> SQL&gt; desc user_info<br style="word-wrap:break-word"> 名称&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;是否为空? 类型<br style="word-wrap:break-word"> ----------------------------------------- -------- ----------------------------<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> ID&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; NUMBER<br style="word-wrap:break-word"> CODE&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;VARCHAR2(10)<br style="word-wrap:break-word"> NAME&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;VARCHAR2(20)<br style="word-wrap:break-word"> FDATE&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; DATE<br style="word-wrap:break-word"> REMARK&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;VARCHAR2(50)<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 在name,fdate上建立复合索引。<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> select name,fdate from user_info where fdate=trunc(sysdate)<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 这样可以利用到索引，如果查询中还有别的列，那么就不行了！<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 一般我们认为like '%xx%'是不会走索引的，可是如果只查询了索引列或count等，还是可以利用索引的！</td> 
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       <span style="word-wrap:break-word">发表于 2007-11-15 21:52</span>&nbsp; 
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            <blockquote style="word-wrap:break-word; display:inline-block; margin:0px; padding:0px 65px 5px 0px; line-height:1.6; zoom:1"> 
             <span style="word-wrap:break-word">最初由 hanjs 发布</span> 
             <br style="word-wrap:break-word"> [B] 
             <br style="word-wrap:break-word"> 
             <br style="word-wrap:break-word"> 这个要看sql怎么写的。 
             <br style="word-wrap:break-word"> 
             <br style="word-wrap:break-word"> SQL&gt; desc user_info 
             <br style="word-wrap:break-word"> 名称&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;是否为空? 类型 
             <br style="word-wrap:break-word"> ----------------------------------------- -------- ---------------------------- 
             <br style="word-wrap:break-word"> 
             <br style="word-wrap:break-word"> ID&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; NUMBER 
             <br style="word-wrap:break-word"> CODE&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;VARCHAR2(10) 
             <br style="word-wrap:break-word"> NAME&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;VARCHAR2(20) 
             <br style="word-wrap:break-word"> FDATE&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; DATE 
             <br style="word-wrap:break-word"> REMARK&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;VARCHAR2(50) 
             <br style="word-wrap:break-word"> 
             <br style="word-wrap:break-word"> 在name,fdate上建立复合索引。 
             <br style="word-wrap:break-word"> 
             <br style="word-wrap:break-word"> select name,fdate from user_info where fdate=trunc(sysdate) 
             <br style="word-wrap:break-word"> 
             <br style="word-wrap:break-word"> 这样可以利用到索引，如果查询中还有别的列，那么就不行了！ 
             <br style="word-wrap:break-word"> 
             <br style="word-wrap:break-word"> 一般我们认为like '%xx%'是不会走索引的，可是如果只查询了索引列或count等，还是可以利用索引的！ [/B] 
            </blockquote> 
           </div> <br style="word-wrap:break-word"> <br style="word-wrap:break-word"> SQL&gt; create table test1(id int,code varchar2(20),zode varchar2(10));<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> Table created.<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> SQL&gt; begin<br style="word-wrap:break-word"> &nbsp;&nbsp;2&nbsp; &nbsp;&nbsp;&nbsp;for i in 1..1000 loog<br style="word-wrap:break-word"> &nbsp;&nbsp;3&nbsp;&nbsp;/<br style="word-wrap:break-word"> &nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;for i in 1..1000 loog<br style="word-wrap:break-word"> &nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; *<br style="word-wrap:break-word"> ERROR at line 2:<br style="word-wrap:break-word"> ORA-06550: line 2, column 19:<br style="word-wrap:break-word"> PLS-00103: Encountered the symbol "LOOG" when expecting one of the following:<br style="word-wrap:break-word"> * &amp; - + / at loop mod remainder rem &lt;an exponent (**)&gt; ||<br style="word-wrap:break-word"> multiset<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> <br style="word-wrap:break-word"> SQL&gt; begin<br style="word-wrap:break-word"> &nbsp;&nbsp;2&nbsp; &nbsp;&nbsp;&nbsp;for i in 1..1000 loop<br style="word-wrap:break-word"> &nbsp;&nbsp;3&nbsp; &nbsp;&nbsp;&nbsp;insert into test1 values(i,'xxx'||i,'zode'||i);<br style="word-wrap:break-word"> &nbsp;&nbsp;4&nbsp; &nbsp;&nbsp;&nbsp;end loop;<br style="word-wrap:break-word"> &nbsp;&nbsp;5&nbsp;&nbsp;commit;<br style="word-wrap:break-word"> &nbsp;&nbsp;6&nbsp;&nbsp;end;<br style="word-wrap:break-word"> &nbsp;&nbsp;7&nbsp;&nbsp;/<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> PL/SQL procedure successfully completed.<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> SQL&gt; create index ind_id_code on test1(id,code);<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> Index created.<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> SQL&gt; set autotrace on<br style="word-wrap:break-word"> SQL&gt; set autotrace trace<br style="word-wrap:break-word"> SQL&gt; set autotrace<br style="word-wrap:break-word"> Usage: SET AUTOT[RACE] {OFF | ON | TRACE[ONLY]} [EXP[LAIN]] [STAT[ISTICS]]<br style="word-wrap:break-word"> SQL&gt; set autotrace trace exp<br style="word-wrap:break-word"> SQL&gt; select id,code from test1 where code='xxx10';<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> Execution Plan<br style="word-wrap:break-word"> ----------------------------------------------------------<br style="word-wrap:break-word"> Plan hash value: 3343096337<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> --------------------------------------------------------------------------------<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> ----<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> | Id&nbsp;&nbsp;| Operation&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;| Name&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;| Rows&nbsp;&nbsp;| Bytes | Cost (%CPU)| Time<br style="word-wrap:break-word"> &nbsp; &nbsp;|<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> --------------------------------------------------------------------------------<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> ----<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> |&nbsp; &nbsp;0 | SELECT STATEMENT&nbsp; &nbsp;&nbsp;&nbsp;|&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; |&nbsp; &nbsp;&nbsp;&nbsp;1 |&nbsp; &nbsp; 25 |&nbsp; &nbsp;&nbsp;&nbsp;3&nbsp; &nbsp;(0)| 00:00:<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 01 |<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> |*&nbsp;&nbsp;1 |&nbsp;&nbsp;INDEX FAST FULL SCAN| IND_ID_CODE |&nbsp; &nbsp;&nbsp;&nbsp;1 |&nbsp; &nbsp; 25 |&nbsp; &nbsp;&nbsp;&nbsp;3&nbsp; &nbsp;(0)| 00:00:<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 01 |<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> --------------------------------------------------------------------------------<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> ----<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> <br style="word-wrap:break-word"> Predicate Information (identified by operation id):<br style="word-wrap:break-word"> ---------------------------------------------------<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> &nbsp; &nbsp;1 - filter("CODE"='xxx10')<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> Note<br style="word-wrap:break-word"> -----<br style="word-wrap:break-word"> &nbsp; &nbsp;- dynamic sampling used for this statement<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> SQL&gt;<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 是index fast full scan啊，</td> 
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       <span style="word-wrap:break-word">发表于 2007-11-15 21:59</span>&nbsp; 
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          <td style="word-wrap:break-word; font-size:14px"> SQL&gt; select id,code from test1 where id=10;<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> Execution Plan<br style="word-wrap:break-word"> ----------------------------------------------------------<br style="word-wrap:break-word"> Plan hash value: 2428865550<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> --------------------------------------------------------------------------------<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> | Id&nbsp;&nbsp;| Operation&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;| Name&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;| Rows&nbsp;&nbsp;| Bytes | Cost (%CPU)| Time&nbsp; &nbsp;&nbsp;&nbsp;|<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> --------------------------------------------------------------------------------<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> |&nbsp; &nbsp;0 | SELECT STATEMENT |&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; |&nbsp; &nbsp;&nbsp;&nbsp;1 |&nbsp; &nbsp; 25 |&nbsp; &nbsp;&nbsp;&nbsp;2&nbsp; &nbsp;(0)| 00:00:01 |<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> |*&nbsp;&nbsp;1 |&nbsp;&nbsp;INDEX RANGE SCAN| IND_ID_CODE |&nbsp; &nbsp;&nbsp;&nbsp;1 |&nbsp; &nbsp; 25 |&nbsp; &nbsp;&nbsp;&nbsp;2&nbsp; &nbsp;(0)| 00:00:01 |<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> --------------------------------------------------------------------------------<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> <br style="word-wrap:break-word"> Predicate Information (identified by operation id):<br style="word-wrap:break-word"> ---------------------------------------------------<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> &nbsp; &nbsp;1 - access("ID"=10)<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> Note<br style="word-wrap:break-word"> -----<br style="word-wrap:break-word"> &nbsp; &nbsp;- dynamic sampling used for this statement<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> SQL&gt;<br style="word-wrap:break-word"> 如果这么写就是INDEX RANGE SCAN了，<br style="word-wrap:break-word"> 估计oracle看到sql是只查询id,code这两个字段，index中正好已经包括这两个字段，因此不用scan table了。但是上面一个查询条件是code用不到index 的key因此使用了full index scan，而这个的查询条件是id用到了key，因此使用了index range scan，实际上这两个是不一样的<br style="word-wrap:break-word"> <br style="word-wrap:break-word"> 个人认为，建index的目的是为了让oracle使用index range scan。个人愚见，望大佬指正。</td> 
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