Chuan Zhang,
hei��you statement choose all rows from the table,Of course oracle will use full
table scan!
There is no where clause in your SQL.If you add:
select a,b,c from test where a=some_value, then of course it will use the
index.
Regards
zhu chao
Eachnet DBA
86-21-32174588-667
[EMAIL PROTECTED]
======= 2002-08-29 23:03:00 ,you wrote��=======
>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,
= = = = = = = = = = = = = = = = = = = =
����������������zhu chao
����������������[EMAIL PROTECTED]
��������������������2002-08-30
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