sossisson,

explain plan for with tt as ( select level id from dual connect by level <=100) select * from tt where id in (1,2,3);

Explained.

Elapsed: 00:00:00.01
@utlxpls

PLAN_TABLE_OUTPUT
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Plan hash value: 2403765415

--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 13 | 2 (0)| 00:00:01 |
|* 1 | VIEW | | 1 | 13 | 2 (0)| 00:00:01 |
|* 2 | CONNECT BY WITHOUT FILTERING| | | | | |
| 3 | FAST DUAL | | 1 | | 2 (0)| 00:00:01 |
--------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
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1 - filter("ID"=1 OR "ID"=2 OR "ID"=3)
2 - filter(LEVEL<=100)