Example

gistfile1.sql

SQL> create table tsysdate(dt date);

Table created.
SQL> create function fsysdate return date as begin return sysdate;end;
  2  /

Function created.

SQL> explain plan for select * from tsysdate where fsysdate between dt and dt;

Explained.

SQL> @xplan


PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------
Plan hash value: 804111645

------------------------------------------------------------------------------
| Id  | Operation         | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |          |     1 |     9 |     2   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS FULL| TSYSDATE |     1 |     9 |     2   (0)| 00:00:01 |
------------------------------------------------------------------------------

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

   1 - filter("DT"<="FSYSDATE"() AND "DT">="FSYSDATE"())
-- as you can see, even if "DT" equal fsysdate when oracle compare first predicate, the function can return 
-- another value within second predicate...