How to use an index with the clause 'in '.

Hi all

I have a sql statement with "" * in the clause * "."

for example:
select emp_id from emp where ename in ("vikas", "krishna", "John", "scott");
When I check the plan explain he uses the index here even if the statistics was entered. He always goes for the full table scan.
There is an index created for the ename column.

Please tell me a technique on how to make use of the index here.


Thank you and best regards,
Vikas Krishna

Vikas,

What version of Oracle you are running.
CLAUSE IN will use the index as appropriate.
In your example Optimizer may decide to use FTS (Full Tablle Scan) for various reasons. May be that the table is very small.
SE for example below where he uses an index on the CLAUSE IN...
The essential point being that I made "wide enough" table (in this case including a column of type CHAR) makes use of INDEX more effective than a FTS.

select * from v$version where rownum < 2;
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi

create table bigt (c int, s char(100));

insert into bigt select level, 'X' from dual connect by level < 501;

create index bigt_in1 on bigt (c );

exec dbms_stats.GATHER_TABLE_STATS('SUDHAKAR', 'BIGT');

explain plan for select c,s from bigt
where c in (1,2,3,43,5);

select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

Plan hash value: 238667275

-----------------------------------------------------------------------------------------
| Id  | Operation                    | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |          |     5 |   520 |     3   (0)| 00:00:01 |
|   1 |  INLIST ITERATOR             |          |       |       |            |          |
|   2 |   TABLE ACCESS BY INDEX ROWID| BIGT     |     5 |   520 |     3   (0)| 00:00:01 |
|*  3 |    INDEX RANGE SCAN          | BIGT_IN1 |     5 |       |     2   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   3 - access("C"=1 OR "C"=2 OR "C"=3 OR "C"=5 OR "C"=43)

VR,
Sudhakar B.

Tags: Database

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