Using criteria on date ranges and ignoring times, best method

Question

Where col.date is a date and time datatype, I know that by using:
trunc(col.date) between trunc(sysdate-10) and trunc(sysdate)
or
to_char(col.dat,'YYYYMMDD') between to_char(sysdate-10,'YYYYMMDD') and to_char(sysdate,'YYYYMMDD')
the results will include rows where col.date is between and including sysdate less 10 days and sysdate.
However, this means Oracle will not use any ordinary (ie not function based) index on the table.
I do not want to add another index (it's a transaction table with many transactions per second) and I would like to improve the speed of the query.
I know that it is close to use
col.date between sysdate-10 and sysdate+ (1-1/(60*60*24)) but this will cause missed data.
select sysdate-10 from dual
2007-01-20-14.03.44
But I want to include any transaction on 2007-01-20, before, during and after the time of 14.03.44.
Perhaps I have to either live with the speed problem or create a function based index on trunc(col.dated).
Any comments, thanks?

Answer 1

If you worry about index using why not to use <<datecolumn>> >= trunc(sysdate-10) and <<datecolumn>> < trunc(sysdate+1) ?
SQL> create table t (dt) as select sysdate+10-rownum from dict where rownum <=30;
Table created.
SQL> alter table t add primary key (dt);
Table altered.
SQL> set autotrace on
SQL> select dt from t where trunc(dt) between trunc(sysdate-10) and trunc(sysdate);
DT
20-JAN-07
21-JAN-07
22-JAN-07
23-JAN-07
24-JAN-07
25-JAN-07
26-JAN-07
27-JAN-07
28-JAN-07
29-JAN-07
30-JAN-07
11 rows selected.
Execution Plan
Plan hash value: 209346666
| Id  | Operation        | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT |             |    11 |    99 |     1   (0)| 00:00:01 |
|*  1 |  FILTER          |             |       |       |            |          |
|*  2 |   INDEX FULL SCAN| SYS_C005970 |    11 |    99 |     1   (0)| 00:00:01 |
SQL> select dt from t where dt >= trunc(sysdate-10) and dt < trunc(sysdate+1);
DT
20-JAN-07
21-JAN-07
22-JAN-07
23-JAN-07
24-JAN-07
25-JAN-07
26-JAN-07
27-JAN-07
28-JAN-07
29-JAN-07
30-JAN-07
11 rows selected.
Execution Plan
Plan hash value: 114909756
| Id  | Operation         | Name        | Rows  | Bytes | Cost (%CPU)| Time
|
|   0 | SELECT STATEMENT  |             |    11 |    99 |     1   (0)| 00:00:01
|
|*  1 |  FILTER           |             |       |       |            |
|
|*  2 |   INDEX RANGE SCAN| SYS_C005970 |    11 |    99 |     1   (0)| 00:00:01
|
--------------------------------------------------------------------------------Rgds.