Help me in creatin an index for inequality operator =

Question

Hi Gurus,
I created an index as below
create index bu_eff_from_dt_indx on bu(eff_from_dt)
When I got the execution plan as below for this query
select * from bu
where eff_from_dt = '01-MAR-2006'
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 217 | 28644 | 43 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| BU | 217 | 28644 | 43 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | BU_EFF_FROM_DT_INDX | 217 | | 1 (0)| 00:00:01 |
The same is not working for <= operator.
select * from bu
where eff_from_dt <= '01-MAR-2006'
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 124K| 15M| 566 (3)| 00:00:07 |
|* 1 | TABLE ACCESS FULL| BU | 124K| 15M| 566 (3)| 00:00:07 |
The total records in this table is more than 2 lacs ..
Please help me to resolve this issue either by index or by partition or any other ..

Answer 1

An example:
SQL> drop table test;
Table dropped.
SQL> create table test as select * from all_objects;
Table created.
SQL> select count(*) from test;
  COUNT(*)
      9304
SQL> create index test_idx on test(object_id);
Index created.
SQL> analyze table test compute statistics;
Table analyzed.
SQL> set autotrace traceonly exp
SQL> select * from test where object_id = 1542;
Execution Plan
Plan hash value: 1389866015
| Id  | Operation                   | Name     | Rows  | Bytes | Cost (%CPU)| Ti
me     |
|   0 | SELECT STATEMENT            |          |     1 |    76 |     2   (0)| 00
:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST     |     1 |    76 |     2   (0)| 00
:00:01 |
|*  2 |   INDEX RANGE SCAN | TEST_IDX |     1 |       |     1   (0)| 00
:00:01 |
Predicate Information (identified by operation id):
   2 - access("OBJECT_ID"=1542)
SQL> select * from test where object_id < 1542;
Execution Plan
Plan hash value: 1389866015
| Id  | Operation                   | Name     | Rows  | Bytes | Cost (%CPU)| Ti
me     |
|   0 | SELECT STATEMENT            |          |  1396 |   103K|    24   (0)| 00
:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST     |  1396 |   103K|    24   (0)| 00
:00:01 |
|*  2 |   INDEX RANGE SCAN | TEST_IDX |  1396 |       |     4   (0)| 00
:00:01 |
Predicate Information (identified by operation id):
   2 - access("OBJECT_ID"<1542)
SQL> select * from test where object_id < 5000;
Execution Plan
Plan hash value: 1357081020
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |      |  4529 |   336K|    36   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS FULL| TEST |  4529 |   336K|    36   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - filter("OBJECT_ID"<5000)
SQL>