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    <p>I have to say that I do not see the same behaviour in 11.2</p> <p>If I set up a test case as follows and updated from 10k to 1m rows in response to Vincent's comment</p> <pre><code>set linesize 130 set pagesize 0 create table mytable ( sdate date ); Table created. insert into mytable select sysdate - level from dual connect by level &lt;= 1000000; commit; 1000000 rows created. Commit complete. alter table mytable add constraint pk_mytable primary key ( sdate ) using index; Table altered. begin dbms_stats.gather_table_stats( user, 'MYTABLE' , estimate_percent =&gt; 100 , cascade =&gt; true ); end; / PL/SQL procedure successfully completed. </code></pre> <p>Then, executing your queries I get <em>almost</em> identical looking explain plans (notice the different types of INDEX FULL SCAN) </p> <pre><code>explain plan for select min(sdate) from mytable; Explained. select * from table(dbms_xplan.display); Plan hash value: 3877058912 ----------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 8 | 1 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 8 | | | | 2 | INDEX FULL SCAN (MIN/MAX)| PK_MYTABLE | 1 | 8 | 1 (0)| 00:00:01 | ----------------------------------------------------------------------------------------- 9 rows selected. explain plan for select min(sdate), max(sdate) from mytable; Explained. select * from table(dbms_xplan.display); Plan hash value: 3812733167 ------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 8 | 252 (0)| 00:00:04 | | 1 | SORT AGGREGATE | | 1 | 8 | | | | 2 | INDEX FULL SCAN| PK_MYTABLE | 1000K| 7812K| 252 (0)| 00:00:04 | ------------------------------------------------------------------------------- 9 rows selected. </code></pre> <p>To quote from a previous answer of mine:</p> <blockquote> <p>The two most common reasons for a query not using indexes are:</p> <ol> <li>It's quicker to do a full table scan.</li> <li>Poor statistics.</li> </ol> </blockquote> <p>Unless there's something you're not posting in the question my immediate answer would be that you have not collected statistics on this table, you haven't collected them with a high enough estimate percent or you've used <a href="http://docs.oracle.com/cd/E11882_01/server.112/e26088/statements_4005.htm#SQLRF01105" rel="nofollow"><code>analyze</code></a>, which will <em>not</em> help the Cost Based Optimizer, unlike <a href="http://docs.oracle.com/cd/E11882_01/server.112/e25494/general002.htm#ADMIN11525" rel="nofollow"><code>dbms_stats.gather_table_stats</code></a>.</p> <p>To quote from the documentation on <code>analyze</code>:</p> <blockquote> <p>For the collection of most statistics, use the DBMS_STATS package, which lets you collect statistics in parallel, collect global statistics for partitioned objects, and fine tune your statistics collection in other ways. See Oracle Database PL/SQL Packages and Types Reference for more information on the DBMS_STATS package. </p> <p>Use the ANALYZE statement (rather than DBMS_STATS) for statistics collection not related to the cost-based optimizer:</p> </blockquote>
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    1. COI've just seen you comment stating 100k rows but re-doing this with that amount makes no difference.
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    2. COI provided data in my post. I also did it myself again and got the same results with 11.1.
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    3. CO10k is puny :) try with 1M rows, you should see a difference
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      1. USVincent Malgrat
 

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