Re: Why does this query need a table access by rowid?

From: Tanel Põder <tanel.poder.003_at_mail.ee>
Date: Fri, 23 Jul 2004 21:29:12 +0300
Message-ID: <35b401c470e2$f42c72d0$0a879fd9@porgand>

> > Try to do a composite index on f(doc_id), doc_id.
>
> (I did hit send too early..)
> Of course this kind of composite index would eliminate the benefit of
having
> smaller index, since all doc-ids would be stored in index anyway...

I did hit send too early again :)

Try this:

SQL> create table t (a number, b number, status char(1));

Table created.

SQL>
SQL> create index i on t(decode(status, 'Y', a, null));

Index created.

SQL> analyze table t compute statistics;

Table analyzed.

SQL>
SQL> select /*+ INDEX(t i) */ decode(status, 'Y', a, null) from t where decode(status, 'Y', a, null) = 1;

no rows selected

SQL>
SQL> @x
SQL> set termout off

PLAN_TABLE_OUTPUT

|   0 | SELECT STATEMENT     |             |     1 |    16 |     2  (50)|
|*  1 |  INDEX RANGE SCAN    | I           |     1 |    16 |     2  (50)|
-------------------------------------------------------------------------

Predicate Information (identified by operation id):

1 - access(DECODE("T"."STATUS",'Y',"T"."A",NULL)=1) SQL> Applying the function to the column you're selecting will make use of the index...

Tanel.

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Received on Fri Jul 23 2004 - 13:25:57 CDT