Re: Function Based Index - Not Used ???

JP,

In the EXPLAIN PLAN, it says "Card=262146", indicating that the query expects to retrieve over a quarter-million rows. Is that in fact correct?

If so, the CBO is making the correct decision to perform a FULL table scan. What was the comparison of elapsed times between the two plans, the one being the FULL table scan and the other being the indexed scan? I bet the FULL table scan query finished much more quickly...

You've got everything configured correctly -- simply a lousy index. The CBO has to be coerced into using the index because it is not the best plan to use.

Hope this helps...

-Tim

on 5/28/03 11:54 PM, Prem Khanna J at jprem_at_kssnet.co.jp wrote:

> Guys,
>
> create table Tab1 ( name varchar2(100),age int,state varchar2(100),country
> varchar2(100));
>
> insert into tab1 values ('SCOTT',25,'TN','India');
>
> I have 20,00,000 records like above.
>
> create index idx1 on tab1 (upper(name));
>
> analyze table tab1 compute statistics;
> analyze index idx1 compute statistics;
>
> select age from tab1 where upper(name)='SCOTT'; ---> this will return around
> 50 records.
>
> ---------------------------------------------------------
> 0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2458 Card=262146 Bytes=2097168)
> 1 0 TABLE ACCESS (FULL) OF 'TAB1' (Cost=2458 Card=262146 Bytes=2097168)
>
> --- INIT.ORA ----------------------
> optimizer_mode=choose
> compatible=8.1.0
> query_rewrite_enabled=true
> query_rewrite_integrity=trusted
> -----------------------------------
> It's Oracle 8.1.6/Win2K.
>
> When i add a HINT, IDX1 is used.Why is it so ?
> Why this SELECT does not use index IDX1 w/o a hint ?
>
> TIA.
> Jp.
>

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Author: Tim Gorman
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