"Tables are not using indexes"-Please help

Question

We have a new database , version
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - 64bi
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for IBM/AIX RISC System/6000: Version 10.2.0.1.0 - Productio
NLSRTL Version 10.2.0.1.0 - Production
We have created Indexes for the tables and analysed the table. Problem is , non of the tables are using indexes. Explain paln for the sql queries are showing full table scan.
Kindly let me know any parameter I have to change or is there any setttings needed on database level?
Thanks in advance.
Regards,
Chotu

Answer 1

What is your optimizer mode?
Another question why you want to use indexes? Use of indexes depends,
Here is a simple example
test@>ed
Wrote file afiedt.buf
  1  explain plan for
  2  select c.cname from mytable c, mytable1 m
  3* where c.cname=m.cname
test@>/
Explained.
test@>SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY());
PLAN_TABLE_OUTPUT
Plan hash value: 2460944079
| Id  | Operation         | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |              |     8 |    64 |     1   (0)| 00:00:01 |
|   1 |  NESTED LOOPS     |              |     8 |    64 |     1   (0)| 00:00:01 |
|   2 |   INDEX FULL SCAN | C_MYTAB_IDX  |     8 |    32 |     1   (0)| 00:00:01 |
|*  3 |   INDEX RANGE SCAN| C_MYTAB1_IDX |     1 |     4 |     0   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   3 - access("C"."CNAME"="M"."CNAME")
15 rows selected.
test@>explain plan for
  2  select * from mytable;
Explained.
test@>SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY());
PLAN_TABLE_OUTPUT
Plan hash value: 1229213413
| Id  | Operation         | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |         |     8 |    32 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| MYTABLE |     8 |    32 |     3   (0)| 00:00:01 |
8 rows selected.As you see MYTABLE has an index but it not always uses that index it depends on the need.
sql queries are showing full table scan this is a not a curse. So unless you are having some problem. You should not change queries only because to avoid full table scans, there is no rule that indexes should always be used in every case.
Adith