I am confused with this CBO issuse

From: Evan Cao <ecao_at_ti.com>
Date: Mon, 19 Oct 1998 22:05:24 -0600
Message-ID: <362C0C04.5DB5BBD6@ti.com>

scenario:

SELECT NUM_ROWS, LAST_ANALYZED FROM DBA_TABLES WHERE TABLE_NAME='XXX'; 0 SEPT-24-98 select count(*) from xxx;

1310000

There is an unique index on table xxx on column say index_0 on xxx(c1,c2);

Observation:

select * from xxx where c1=:a and c2=:b;

Noticed by an SAP monitor, ORACLE is doing a full table read, taking long time, which is understandable. what I am confused is that when I explain this stmt. I see ORACLE using the index index_0

What's wrong here??? What is the logical explaination here?

BTW. how can we find out ORACLE is doing a full table scan without using sql trace?

Thx

Received on Mon Oct 19 1998 - 23:05:24 CDT