RE: Index hints?

From: Khedr, Waleed <Waleed.Khedr_at_FMR.COM>
Date: Sun, 01 Sep 2002 18:18:19 -0800
Message-ID: <F001.004C53A0.20020901181819@fatcity.com>

There is nothing wrong in having a comma in a hint:

SQL> create table test_hint ( c1 number not null , c2 number);

Table created.

SQL>
SQL> create index testix1 on test_hint (c1);

Index created.

SQL> 
SQL> set autotrace on explain;
SQL> 
SQL> select * from test_hint a;

no rows selected

Execution Plan

0 SELECT STATEMENT Optimizer=CHOOSE 1 0 TABLE ACCESS (FULL) OF 'TEST_HINT' SQL>
SQL> select /*+ index(a,testix1) */ * from test_hint a;

no rows selected

Execution Plan

   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=826 Card=164 Bytes=4
          264)

   1    0   TABLE ACCESS (BY INDEX ROWID) OF 'TEST_HINT' (Cost=826 Car
          d=164 Bytes=4264)

   2    1     INDEX (FULL SCAN) OF 'TESTIX1' (NON-UNIQUE) (Cost=26 Car
          d=164)

Regards,

Waleed

-----Original Message-----
Sent: Sunday, September 01, 2002 9:28 PM To: Multiple recipients of list ORACLE-L

Thanks all the responses.

It's the syntax error like Naveen said. Oracle didn't detect the error, it just simply ignore the hints if the syntax is wrong.

Thanks again,

Chuan
-----Original Message-----
Sent: Friday, 30 August 2002 5:33 PM
To: Multiple recipients of list ORACLE-L

If you specify a hint Oracle is forced to use the index.

Your hint's syntax is wrong. USE - /*+ INDEX(test index_a) */

Don't use the comma ******* between the table name and the index name

Naveen

-----Original Message-----
Sent: Friday, August 30, 2002 12:33 PM
To: Multiple recipients of list ORACLE-L

Hi, All,

On a million row table, test, there is primary key on column a.

when I run select /*+ index (test,indx_a) */ a, b, c, from test, according to Oracle, I should get the following explain plan. TABLE ACCESS
BY INDEX ROWID test 1
INDEX
UNIQUE SCAN PK_test 1

But I acctucally got :
TABLE ACCESS

FULL                           test                              1

The database optimizer mode is choose, and I gathered the statistics on table and index using dbms_utitlity and analyze. In the session level, I also set optimizer_mode=first_rows to push optimizer to choose the index.
According to Oracle Doc "use hints to force the optimizer to use the optimal execution plan.", to my understanding, the explain plan under such a situation, should be the first one.

Does Oracle follow the hint? or to waht extents, it follows?

Appreciated if someone guides me to the right direction.

Chuan,

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Author: Naveen Nahata
INET: naveen_nahata_at_mindtree.com

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Author: Khedr, Waleed
INET: Waleed.Khedr_at_FMR.COM

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