Today i saw the following post on OTN
“select *
from customer c
inner join work_item sp1 ON sp1.customer_id = c.customer_id
and I am using TOAD, which tells me (in the Explain Plan area), that I’m doing a “TABLE ACCESS FULL” scan on the customer table.
But when I look at the details of BOTH tables, I can clearly see that they both have an index on the customer field, and they are both the same data types…”
And my answer was:
One of the main reason of existence of index if to FILTER information.
But you didn´t gave any filter conditions, you jus gave join conditions, so Oracle should be ordered both table with Hash join or Merge Join.
And it probally is faster than using index.
If you can create a filter condition, and this column have a index on it , Oracle can use it.