Efficient way to retrieve just today's data ?

Question

I'm wondering what the best way in Oracle is to retreive just records created with todays date. There may be millions of rows, but only a thousand or so for today. I'm thinking an index on the timestamp column, and a query that would cause an index range scan. Something like where someColumn >= trunc(sysdate) and someColumn < trunc(sysdate)+1
Is there a better way than this ? Example:
--Create some dummy test data, and index the datetime column
CREATE TABLE t (id number,dt TIMESTAMP(6));
INSERT INTO t SELECT rownum, sysdate - mod(rownum,10000) FROM all_objects;
commit;
CREATE INDEX t_idx1 ON t(dt);
--query that uses index
select * from t where dt >= trunc(sysdate) and dt < trunc(sysdate)+1

Answer 1

The function based index seems slightly more efficient (less steps in execution plan):
SQL> CREATE TABLE t (ID NUMBER,dt TIMESTAMP(6));
Table created.
SQL> INSERT INTO t
  2     SELECT ROWNUM, SYSDATE - MOD (ROWNUM, 10000)
  3       FROM all_objects;
47489 rows created.
SQL>
SQL> CREATE INDEX t_idx1 ON t(dt);
Index created.
SQL> CREATE INDEX t_idx2 ON t(TRUNC(dt));
Index created.
SQL>
SQL> EXEC dbms_stats.GATHER_TABLE_STATS(user,'t',cascade=>true)
PL/SQL procedure successfully completed.
SQL>
SQL> SET linesize 200
SQL> SET autotrace traceonly explain statistics
SQL> SET timing on
SQL> SELECT *
  2    FROM t
  3   WHERE dt >= TRUNC (SYSDATE) AND dt < TRUNC (SYSDATE) + 1;
Elapsed: 00:00:00.01
Execution Plan
Plan hash value: 2411712980
| Id  | Operation                    | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT             |        |     7 |   112 |    10   (0)| 00:00:01 |
|*  1 |  FILTER                      |        |       |       |            |          |
|   2 |   TABLE ACCESS BY INDEX ROWID| T      |     7 |   112 |    10   (0)| 00:00:01 |
|*  3 |    INDEX RANGE SCAN          | T_IDX1 |     7 |       |     2   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - filter(TRUNC(SYSDATE@!)<TRUNC(SYSDATE@!)+1)
   3 - access("DT">=TRUNC(SYSDATE@!) AND "DT"<TRUNC(SYSDATE@!)+1)
Statistics
          1  recursive calls
          0  db block gets
          7  consistent gets
          0  physical reads
          0  redo size
        520  bytes sent via SQL*Net to client
        381  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          4  rows processed
SQL>
SQL>
SQL> SELECT *
  2    FROM t
  3   WHERE TRUNC (dt) = TRUNC (SYSDATE)
  4  /
Elapsed: 00:00:00.01
Execution Plan
Plan hash value: 3371054274
| Id  | Operation                   | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT            |        |     5 |    80 |     6   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T      |     5 |    80 |     6   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | T_IDX2 |     5 |       |     1   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   2 - access(TRUNC(INTERNAL_FUNCTION("DT"))=TRUNC(SYSDATE@!))
Statistics
          1  recursive calls
          0  db block gets
          7  consistent gets
          0  physical reads
          0  redo size
        520  bytes sent via SQL*Net to client
        381  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          4  rows processed